In blogger when write post there is part for search descriptions that used by google search to show what is your post is all about. Also blogger search description can be used as tool for organic traffics for you blog so as to increase more traffic as way of increasing income from Google Adsense or other monetization sites
How To Add post Description in search Description
When Writing a blog post in the right side of your blogger dashboard there is two search Icon the first one is the search description Icon the next one for custom robot tags
So you have to choose the first one so as to had useful keywords that all about written post so as to gain more organic traffic for your blog.
Thus a search description is basically a sentence that holds the post keywords and a short description of the content of your blog post for SEO so as to rank in google search
You are advised to use about 150 characters in search Description.
What will happen incase you forget to add search description
Google will had automatically few line of your blog post that will appear in google search incase people search related article of your blog.