Step 1: Add jQuery plugin (if your blog has jquery, ignore this step)
- Go to Design->Edit HTML[Template->Edit HTML in new blogger interface]
- Copy & paste code below just after or below <head> tag
<script src='http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js'
type='text/javascript'/>
- Now Go to Design-> Page Elements
- Click add gadget and select HTML/javascript
- Copy and paste the generated code inside it and save it.