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 .

<style type='text/css'>
#tabs24 {
 float:left;
 width:100%;
 background:#BBD9EE;
 font-size:93%;
 line-height:normal;
 }
#tabs24 ul {
margin:0;
padding:10px 10px 0 50px;
list-style:none;
 }
#tabs24 li {
 display:inline;
 margin:0;
 padding:0;
 }
#tabs24 a {
 float:left;
 background:url(http://3.bp.blogspot.com/_4HKUHirY_2U/SwIsrl_4pRI/AAAAAAAAAMM/6ekfoySymgo/left.gif) no-repeat left top;
 margin:0;
 padding:0 0 0 4px;
 text-decoration:none;
 }
#tabs24 a span {
 float:left;
 display:block;
 background:url(http://1.bp.blogspot.com/_4HKUHirY_2U/SwIsvQdvAVI/AAAAAAAAAMU/7BhI82yCGpo/right.gif) no-repeat right top;
 padding:5px 15px 4px 6px;
 color:#666;
 }

#tabs24 a span {float:none;}
/* End IE5-Mac hack */
#tabs a:hover span {
 color:#FF9834;
 }
#tabs24 a:hover {
 background-position:0% -42px;
 }
#tabs24 a:hover span {
 background-position:100% -42px;
 }
</style>

Note : Please Host above 2 images yourself.

4.Save your template.

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

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

<div id="tabs24">

<ul>
<li><a href="#"><span>Home</span></a></li>
<li><a href="#"><span>HTML</span></a></li>
<li><a href="#"><span>CSS</span></a></li>
<li><a href="#"><span>Java Script</span></a></li>
<li><a href="#"><span>About</span></a></li>
<li><a href="#"><span>Contact</span></a></li>
<li><a href="#"><span>Privacy Policy</span></a></li>
</ul>

</div>

7.Now you are done.It will look like this:

Horizontal CSS Menu Tutorial to blogger