Direct Input help

Hi everyone,
I'm a total beginner in C and for sure in C++.
I am trying to send virtual key presses and mouseclicks to a game, I tried it with commands like SendInput SendMessage or PostMessage but it didn't work, because the game seems to use direct input.
Now I wonder, if there is a simple way in C/C++ to get my programm to work with this game.
Please remember that I'm a real beginner so please explain everything detailed.^^

I'm looking forward to get your help and suggestions

First you have to make sure the game is using DirectInput. If it is (IIRC), PostMessage should work (read the documentation for proper lParam/wParam assignment).

Or you could hook the correct interface method of DirectInput itself.

There are many API which send messages / do output, SendMessage, PostMessage, keybd_event, mouse_event, SendInput etc etc
which of these is the base api?
I mean...internally does SendMessage() call PostMessage() or vice-versa? - what's the lowest level API that doesn't call any other api?
I've been using keybd_event which works for the games I play, but I've always been curious about the above question, but since keybd_event has always worked for me, I've never really learned about the other api's. Thanks.