Ok, I’m just a beginner, so this will probably be a simple answer, but I just can’t find it.
How can I make that the player can click a 3D object and the game executes some code?
For example, some object lies on the floor, I want to make that when the player clicks it it displays “Object picked up.”
How?
And this ‘picking’ (up) would be exactly the terms you are looking for 
Try this one 
For a better intuitive understanding however, I’d recommend you to do a few things with the existing samples, using what you read in the manual on collision detection.
Thanks a lot!