Want to create a wrapper class for dlopen, dlsym, dlclose to work on both UNIX and windows platform

I would like to create a wrapper class to dynamic load dll.
I know I need to at least support dlopen, dlsym, dlclose for UNIX

On windows, I believe LoadLibrary() == dlopen()
GetProcAddress() == dlsym()
and FreeLibrary() == dlclose()

Is this correct?

In LoadLibrary() windows function, it return HINSTANCE type.
In dlopen(),  it return void*

So what is HINSTANCE type is?  
I need some help to write this wrapper class, can someone provide a simple function, maybe just shows me how to write the wrapper function for dlopen and LoadLibrary()?

Also, what other functions I need to be cover in this wrapper other than the dlopen, dlclose, dlsym()?  Did I miss anything?

What heppen if I called dlopen and never call dlcose?  This question has nothing to do with my wrapper class, but I just want to under this a bit better.

Thanks.
4eyes