Report Print Format

Can Anyone Help me?
How to use the Print format For Report.

If I go in Print Format, I can see the Option of Print Format For [Report,Doctype].
We I select Report. then How to Use it , where to use it.

@Sudhanshu open report General Ledger and press print

I already tried that.
i get this kind of error.

Maybe @ejaaz from Frappe Team can help with this one.