How can I know what is inside DLL and how to make use that function.

This information is usually not stored in the DLL.

If the DLL exports C++ style functions, you may be able to deduce the arguments from the name mangling.  The mangled names will look really weird (e.g.: ?Func@@YAHN@Z) and the name mangling scheme is different for each compiler.It is not well documented but you can find some info here: http://www.kegel.com/mangle.html

Otherwise, if the functions use the __stdcall Windows calling convention, they will only expose the number of bytes that the arguments need.  That does not give you much as func@8 could be either of:
    void func(double)
    int* func(float, unsigned long)
    etc...

Otherwice, the standard C calling convention does not save any information about the arguments.

On top of that, the functions in the DLL may have been renamed by a .DEF file.

To summarize: you're out of luck

in a dll there's no information stored about the parameters a function uses. however, some dlls written in c++ follow a naming convention which adds a '@' to the functions name followed by the parameter size in hex.
of course, this does not help you.
when you want to use a dll in vc++ 6, you need the .lib assigned to the dll. add it's name ander project settings, link. most of the windows dll's libs are shiped with vc++.

Hi alexo
Can I have "some" good example for DLL usage code,it may much help me to make understand.
Waiting for you alexo.
Thnaks in advance
bringmetoyourwolrd

Sorry bringmetoyourworld, I'm not sure I understand what you want.  Could you elaborate?

Hi alexo
I have recieved a DLL from internet and I want to make use it,and I am a beginner .I want to know what is inside that DLL and how to use that function .Do you have the example code for using DLL.
A lot of thanks.

Hi alexo
I found some information about that DLL .You are right,
Thank you.