I'll just put the link here, he explain better than me.
After you read that very well made post, you probably want to understand why I made this thread, well the main reason is this :
https://github.com/tomrus88/WowAddin this is a very powerful tool and god so amazing, i'm using it for GM command ( which I will release whenever i'm done with it)
so yeah if you want to extend your knowledge in c++ and understand how your favorite emulator work in the same time, do not look any further !
What's WowAddin ? WowAddin is a DLL that extend functionnality (see Command.cpp)