Hello,
Can anyone give me a program code of the following: When I press E with the mouse cursor on an entity, the game picks it up, so we can move it with the mouse and with WASD keys. But when we press left mouse button, the game drops the entity away. Or if we press E again, the game puts the entity down. It's like in Half-Life 2. So, if anyone could give me a program code for this, I would be very thankful.

Most likely not. You can however try to do this on your own and ask for questions if you encounter specific problems with your implementation. Alternatively, pX_pick() may be a starting point.

So, I have to do this on my own. Maybe I've asked too much. Thanks anyway!