What do you mean by framework of a programming language?

Question

I mean what are its functions and why it is used and how do we know what all things it can do?

Answer 1

Framework is a kind of a programming environment. It provides a standard within which you can create codes or applications, especially of similar purpose (web-related, OS-compatible and such).
You know what is what by studying documentation or taking an adequate course online. Usually powerful and popular frameworks have strong communities which may be helpful as well.