collision in game

collision in game

how do collision is calculated in game?

so that characters dont fall through the floor, stop at walls, and not clip in? maybe also walk on tilted floors and be angled?

do they use placeholders to test the physics? of what kind?

how are these dones, by example, C++ or pythons? C#? lisp?
logically, where are the parameters written between object to object so things connect?