Crawl errors showing up in google webmasters

[Jasjot Singh]

Hey guys there are always some kind of errors showing up in my google wemasters account.

some crawl errors says links not found but i wonder i haven't build those URL's.

and someare build such as sites feed but still showing not found.

what should i do with these errors, should i keep them intact or what.
will it affect my sites rankings.