1.Login to your blogger dashboard--> layout- -> Edit HTML

2.Scroll down to where you see </head> tag .

3.Copy below code and paste it just before the </head> tag.

<script type='text/javascript'>
//<![CDATA[

//** Tab Content script v2.0- © Dynamic Drive DHTML code library (http://www.dynamicdrive.com)
//** Updated Oct 7th, 07 to version 2.0. Contains numerous improvements:
//   -Added Auto Mode: Script auto rotates the tabs based on an interval, until a tab is explicitly selected
//   -Ability to expand/contract arbitrary DIVs on the page as the tabbed content is expanded/ contracted
//   -Ability to dynamically select a tab either based on its position within its peers, or its ID attribute (give the target tab one 1st)
//   -Ability to set where the CSS classname "selected" get assigned- either to the target tab's link ("A"), or its parent container
//** Updated Feb 18th, 08 to version 2.1: Adds a "tabinstance.cycleit(dir)" method to cycle forward or backward between tabs dynamically
//** Updated April 8th, 08 to version 2.2: Adds support for expanding a tab using a URL parameter (ie: http://mysite.com/tabcontent.htm?tabinterfaceid=0)

////NO NEED TO EDIT BELOW////////////////////////

function ddtabcontent(tabinterfaceid){
this.tabinterfaceid=tabinterfaceid //ID of Tab Menu main container
this.tabs=document.getElementById(tabinterfaceid).getElementsByTagName("a") //Get all tab links within container
this.enabletabpersistence=true
this.hottabspositions=[] //Array to store position of tabs that have a "rel" attr defined, relative to all tab links, within container
this.currentTabIndex=0 //Index of currently selected hot tab (tab with sub content) within hottabspositions[] array
this.subcontentids=[] //Array to store ids of the sub contents ("rel" attr values)
this.revcontentids=[] //Array to store ids of arbitrary contents to expand/contact as well ("rev" attr values)
this.selectedClassTarget="link" //keyword to indicate which target element to assign "selected" CSS class ("linkparent" or "link")
}

ddtabcontent.getCookie=function(Name){
var re=new RegExp(Name+"=[^;]+", "i"); //construct RE to search for target name/value pair
if (document.cookie.match(re)) //if cookie found
return document.cookie.match(re)[0].split("=")[1] //return its value
return ""
}

ddtabcontent.setCookie=function(name, value){
document.cookie = name+"="+value+";path=/" //cookie value is domain wide (path=/)
}

ddtabcontent.prototype={

expandit:function(tabid_or_position){ //PUBLIC function to select a tab either by its ID or position(int) within its peers
this.cancelautorun() //stop auto cycling of tabs (if running)
var tabref=""
try{
 if (typeof tabid_or_position=="string" && document.getElementById(tabid_or_position).getAttribute("rel")) //if specified tab contains "rel" attr
  tabref=document.getElementById(tabid_or_position)
 else if (parseInt(tabid_or_position)!=NaN && this.tabs[tabid_or_position].getAttribute("rel")) //if specified tab contains "rel" attr
  tabref=this.tabs[tabid_or_position]
}
catch(err){alert("Invalid Tab ID or position entered!")}
if (tabref!="") //if a valid tab is found based on function parameter
 this.expandtab(tabref) //expand this tab
},

cycleit:function(dir, autorun){ //PUBLIC function to move foward or backwards through each hot tab (tabinstance.cycleit('foward/back') )
if (dir=="next"){
 var currentTabIndex=(this.currentTabIndex<this.hottabspositions.length-1)? this.currentTabIndex+1 : 0
}
else if (dir=="prev"){
 var currentTabIndex=(this.currentTabIndex>0)? this.currentTabIndex-1 : this.hottabspositions.length-1
}
if (typeof autorun=="undefined") //if cycleit() is being called by user, versus autorun() function
 this.cancelautorun() //stop auto cycling of tabs (if running)
this.expandtab(this.tabs[this.hottabspositions[currentTabIndex]])
},

setpersist:function(bool){ //PUBLIC function to toggle persistence feature
 this.enabletabpersistence=bool
},

setselectedClassTarget:function(objstr){ //PUBLIC function to set which target element to assign "selected" CSS class ("linkparent" or "link")
this.selectedClassTarget=objstr || "link"
},

getselectedClassTarget:function(tabref){ //Returns target element to assign "selected" CSS class to
return (this.selectedClassTarget==("linkparent".toLowerCase()))? tabref.parentNode : tabref
},

urlparamselect:function(tabinterfaceid){
var result=window.location.search.match(new RegExp(tabinterfaceid+"=(\\d+)", "i")) //check for "?tabinterfaceid=2" in URL
return (result==null)? null : parseInt(RegExp.$1) //returns null or index, where index (int) is the selected tab's index
},

expandtab:function(tabref){
var subcontentid=tabref.getAttribute("rel") //Get id of subcontent to expand
//Get "rev" attr as a string of IDs in the format ",john,george,trey,etc," to easily search through
var associatedrevids=(tabref.getAttribute("rev"))? ","+tabref.getAttribute("rev").replace(/\s+/, "")+"," : ""
this.expandsubcontent(subcontentid)
this.expandrevcontent(associatedrevids)
for (var i=0; i<this.tabs.length; i++){ //Loop through all tabs, and assign only the selected tab the CSS class "selected"
 this.getselectedClassTarget(this.tabs[i]).className=(this.tabs[i].getAttribute("rel")==subcontentid)? "selected" : ""
}
if (this.enabletabpersistence) //if persistence enabled, save selected tab position(int) relative to its peers
 ddtabcontent.setCookie(this.tabinterfaceid, tabref.tabposition)
this.setcurrenttabindex(tabref.tabposition) //remember position of selected tab within hottabspositions[] array
},

expandsubcontent:function(subcontentid){
for (var i=0; i<this.subcontentids.length; i++){
 var subcontent=document.getElementById(this.subcontentids[i]) //cache current subcontent obj (in for loop)
 subcontent.style.display=(subcontent.id==subcontentid)? "block" : "none" //"show" or hide sub content based on matching id attr value
}
},

expandrevcontent:function(associatedrevids){
var allrevids=this.revcontentids
for (var i=0; i<allrevids.length; i++){ //Loop through rev attributes for all tabs in this tab interface
 //if any values stored within associatedrevids matches one within allrevids, expand that DIV, otherwise, contract it
 document.getElementById(allrevids[i]).style.display=(associatedrevids.indexOf(","+allrevids[i]+",")!=-1)? "block" : "none"
}
},

setcurrenttabindex:function(tabposition){ //store current position of tab (within hottabspositions[] array)
for (var i=0; i<this.hottabspositions.length; i++){
 if (tabposition==this.hottabspositions[i]){
  this.currentTabIndex=i
  break
 }
}
},

autorun:function(){ //function to auto cycle through and select tabs based on a set interval
this.cycleit('next', true)
},

cancelautorun:function(){
if (typeof this.autoruntimer!="undefined")
 clearInterval(this.autoruntimer)
},

init:function(automodeperiod){
var persistedtab=ddtabcontent.getCookie(this.tabinterfaceid) //get position of persisted tab (applicable if persistence is enabled)
var selectedtab=-1 //Currently selected tab index (-1 meaning none)
var selectedtabfromurl=this.urlparamselect(this.tabinterfaceid) //returns null or index from: tabcontent.htm?tabinterfaceid=index
this.automodeperiod=automodeperiod || 0
for (var i=0; i<this.tabs.length; i++){
 this.tabs[i].tabposition=i //remember position of tab relative to its peers
 if (this.tabs[i].getAttribute("rel")){
  var tabinstance=this
  this.hottabspositions[this.hottabspositions.length]=i //store position of "hot" tab ("rel" attr defined) relative to its peers
  this.subcontentids[this.subcontentids.length]=this.tabs[i].getAttribute("rel") //store id of sub content ("rel" attr value)
  this.tabs[i].onclick=function(){
   tabinstance.expandtab(this)
   tabinstance.cancelautorun() //stop auto cycling of tabs (if running)
   return false
  }
  if (this.tabs[i].getAttribute("rev")){ //if "rev" attr defined, store each value within "rev" as an array element
   this.revcontentids=this.revcontentids.concat(this.tabs[i].getAttribute("rev").split(/\s*,\s*/))
  }
  if (selectedtabfromurl==i || this.enabletabpersistence && selectedtab==-1 && parseInt(persistedtab)==i || !this.enabletabpersistence && selectedtab==-1 && this.getselectedClassTarget(this.tabs[i]).className=="selected"){
   selectedtab=i //Selected tab index, if found
  }
 }
} //END for loop
if (selectedtab!=-1) //if a valid default selected tab index is found
 this.expandtab(this.tabs[selectedtab]) //expand selected tab (either from URL parameter, persistent feature, or class="selected" class)
else //if no valid default selected index found
 this.expandtab(this.tabs[this.hottabspositions[0]]) //Just select first tab that contains a "rel" attr
if (parseInt(this.automodeperiod)>500 && this.hottabspositions.length>1){
 this.autoruntimer=setInterval(function(){tabinstance.autorun()}, this.automodeperiod)
}
} //END int() function

} //END Prototype assignment

//]]>
</script>

<style type='text/css'>
.btabs{padding:3px 0;margin-left:10px;margin-top:1px;margin-bottom:0;font-family:&#39;Lucida Grande&#39;,&#39;Lucida Sans Unicode&#39;,Sans-serif;font-size:1.1em;list-style-type:none;text-align:left}

#tabbody{width:98%;margin-left:10px;padding:10px 4px;background-color:#1a1a1a;color:#fff;border:1px solid #1a1a1a;margin-top:2px}

.btabs li{display:inline;margin:0}

.btabs li a{text-decoration:none;position:relative;z-index:1;padding:5px 7px;background-color:#828282;border:none;color:#fff;margin-right:-2px;outline: none;}

.btabs li a:visited{color:#fff;}

.btabs li a:hover{text-decoration:none;color:#fff;background-color:#545454}

.btabs li a.selected{color:#c7c7c7;position:relative;top:0}

.btabs li a.selected{background-color:#1a1a1a;color:#fff}

.btabs li a.selected:hover{background-color:#1a1a1a;text-decoration:none}

.tabcontent .sb_comment_author{color:#696969;font-size:10px;}

.tabcontent li{color:#b7b7b7;display:block;padding:5px 6px;border-bottom:1px solid #111;border-top:1px solid #222}

.tabcontent li:hover{}

.tabcontent li a{color:#CDCDCD;text-decoration:none;font-size:11px;outline: none;}

.tabcontent li a:hover{color:#27d;text-decoration:underline}

.tabcontent{display:block;}

.tabcontent{display:none;}

.tabcontent{display:block;}

.tabcontentstyle{border:1px solid gray;width:450px;margin-bottom:1em;padding:10px}

.tabcontent{display:none}

.tabcontent{display:block;}

</style>

4.Now save your template.

5.Go to Layout-->Page Elements and click on "Add a gadget".

6.Select "html/java script" and add the code given below and click save.

<ul id="sidebartabs" class="btabs">

<li><a href="#" class="selected" rel="tab1">Popular Post</a></li>
<li><a href="#" rel="tab2">Recent Posts</a></li>
<li><a href="#" rel="tab3">Other Topics</a></li>

</ul>

<div id="tabbody">

<div id="tab1" class="tabcontent">

<ul>

<!--Enter-Tab-1-Content-Here-->

</ul>

</div>

<div id="tab2" class="tabcontent">

<ul>

<!--Enter-Tab-2-Content-Here-->

</ul>

</div>

<div id="tab3" class="tabcontent">

<ul>

<!--Enter-Tab-3-Content-Here-->

</ul>

</div>

</div>

<script type="text/javascript">
var countries=new ddtabcontent("sidebartabs")
countries.setpersist(true)
countries.setselectedClassTarget("link") //"link" or "linkparent"
countries.init()
</script>

Note:Change tab names as your choice.Replace Enter-Tab-X-Content-Here with your content.

You are done.

Demo