By default, there is no meta description option when you crate your blog in blogger. In fact, there is no option to enter meta description anywhere. What this means? It means that when you search for you blog in search engine, results that you see bellow URL will show blog name, description or last post. For this blog it will look like this. As you can see, there is blog name, part of blog description and small part of last post. Why this is bad? Because meta data is VERY, VERY important for search engines! When search engine start to search for phrase that you typed in, algorithm that is used, first compare url, metadata,etc. So if you do not have meta data on your blog and somebody else has and you have same phrase on both blog/website, his blog/website will showned first. And that is extremely important because lets be realistic - how many times you search for something and go on second or third page of Google search results?
Important thing to know about blogger. Metadata description is not the same as blog description. Blog description field is showned under blog name but considering search engine algorithm that field is not important.
Ok, how to enter metadata description on blogger blog? You have to do it manually by inserting HTML code in your template! How to do this? Go to template/edit template. HTML editor will appear. Find <head> </head> block. Anywhere in this block insert following line
<meta content='DESCRIPTION' name='description'/>
And that is that. It takes time for this changes to take place. Maine reason for this is update of search engines.