Help in Blogger

Hi
I Want To Know What Is This Field In Blogger.

Errors and redirections
Custom Page Not Found ? [Not Set] Edit
Custom Redirects ? no items Edit


Crawlers and indexing
Warning! Use with caution. Incorrect use of these features can result in your blog being ignored by search engines.
Custom robots.txt ? [Disabled] Edit
Custom robots header tags ? [Disabled] Edit



If Any One Can Help Me How To Use This Field With Complete Detail.
I Also Need To Know How To Add h1,h2,h3 Tag in My Code That Is Format.I Know Where To Add But How?



Thanks