How do I enable comments on my blog?

To enable Comments, go to the Settings | Comments tab:
Then select the Show radio button and click Save Settings:
Once Comments are enabled, several more settings appear:

Who Can Comment?

• Only Registered Users: if not logged in already, visitors will be prompted to log into Blogger before leaving a comment. If they don't have an account, they can create one.
• Anyone: anybody in the whole wide world can leave comments
• Only Members of this Blog: only members of the blog (if it's a Team Blog) can leave comments

Default for Posts

• New Posts Have Comments: by default, all new posts have Comments enabled
• New Posts Do Not Have Comments: by default, Comments are disabled on new posts, but can be enabled on a by-post basis:
  

  

Comments Timestamp Format

• The date and time that comments are left will be displayed in the format you choose here.