Meta tags are Simple HTML codes that can describe various factors of your site to the search engine spiders .These factors include web page title ,Description,keywords , language and many others . Though many blogs says that the meta tags don't have any value now , i strongly believe that they can affect SERPS in Google ,Yahoo and Bing . In this case i will help you to add meta tag in a Blogger blog.
Go to your Blogger template Layout and Edit HTML .
Fill the following example meta tag with your details
<meta name="Title" content="Your blog title" />
<meta name="Description" content="this is the description of your Blogger blog" />
<meta name="Keywords" content="Your keywords separated by comma" />
<meta name="Author" content="Author Name" />
<meta name="Language" content="Language of Website" />
<meta name="Copyright" content="© Copyright information" />
<meta name="Revisit-After" content="1 Days" />
<meta name="Robots" content="All" />
Now we are about to add meta tag in Blogger.
Find out the <head> tag and paste your details exactly after that selection.
PN: Keywords in meta tag can help you to bring targeted adsense ads into your blog.