I think you are asking about the search description of your blog.
You can create a custom search description for your blog by following below steps.
1. Login to your Blogger account and click on your blog title to open its dashboard.
2. Then goto settings->search preference.
3. Now you will see 'Description' tab. Edit it and write something about your blog e.g., A blog about Runescape MMORPG game, etc.
4. Then click on save changes.
5. Now submit your blog homepage URL to Google index - https://www.google.com/webmasters/tools/submit-url .