QTP FrameWork:

What is QTP Automation Framework,what is the use of that frame work?

Automation framework is nothing but a set of guidelines designed by expert to accomplish a task in an effective,eficcient and an optimised way.
Automation Framework is a Standard/Procedure/Guidelines/process which is use to Automation Planning with respect to AUT.

There are 4 different types of frame work
1. Linear
2. Modular
3.Keyword
4.Hybrid

Linear Framework: If your application is supposed to Regression run on Local System then this framework is better.
Modular Framework: If AUT is supposed to Regression run in which More than one Action has to be performing for the same script then Modular framework is better. You might be making your test Modular by dividing your test into many re-usable actions and either any action can call any of the action within that test.
Keyword Driven Framework:It sound like business process testing where you might be able to write business logics/code and develop your script and those scripts can be call from outside of your test. Moreover there might be various functions libraries to be build and to be use, Recovery Scenarios, OR maintenance etc will provide your test Reusable.