Proper methods for Walking/rolling over uneven floor

Hi there.
I’m a little lost about this, and I do not know whether it is appropriate to use constraints or physics or something else. So I did not know exactly where to open this thread.

I would like to know what would be the appropriate methods to achieve the following situations in an animation (Automatically, without having to do it frame by frame):

You assume a non-uniform/uneven floor/ground.
1- An insect (supposed rigged) walking on the floor, and that feet do not penetrate the surface.
2- Wheels (eg a car) rolling on the floor.

I only need you suggest me some keywords or some clue regarding the correct methods to do it, that way I can research about it. Anyway, if you know any good tutorial I would be very grateful.