Here's how to put the code:
1. Login blogger.com -> Template -> Edit HTML
2. Find this code <title><data:blog.pageTitle/></title>
3. Copy and paste the following code below code no. 2
<b:if cond='data:blog.url == data:blog.homepageUrl'>
<meta content='Your blog description' name='description' />
<meta content='your keywords' name='keywords' />
</b:if>
<meta content='Your blog description' name='description' />
<meta content='your keywords' name='keywords' />
</b:if>