A fixed header is a header that is in a fixed position. It will be seen in your blog wherever you are in your blog. See an example here.
To add this follow these steps
1st Step : Go to Blogger -> Template -> Edit Html
Copy and pate these lines before the tag :
<style type="text/css">
/* Subin's Blog - http://subinsb.com */
.fixed-header{
overflow: hidden;
position: fixed;
z-index: 999999;
top: 0px;
left: 0px;
right: 0px;
height: <span style="color: red;">76</span>px;
background: <span style="color: red;">#EEE</span>;
}</style>
2nd Step : Go to **Blogger -> Layout **and click on button.
Then Click on button and type these in the content area
<div class="fixed-header" >
<center><h1>Type Your Blog Name Here</h1></center>
</div>
After typing Click on “SAVE” button. That’s it. You should now see a fixed-header in your blog.