Hit test and so!

ok, i have already put up a question regarding some of my personal work but that post is dead. so i might as well post a simplq question. I have found many hittest code that i need which when the object the character can not go past this position or when standing on a platform and the character jumps the character will not fall.so far the codes that i have found are either too long or don’t fully work. So what i am asking for is:
(I am trying to make a game by the way)

  1. what simple hittest code can i use were when the character hits the object from the left, right bottom, or above it will not be able to go past it.
  2. and can you make it so that when the character jumps and comes back to land it does not fall through the object OR get stuck half way like when you slightly go of the edge and then you wiz bak buit end up inside the object.

HOPE THIS IS CLEAR
AND HOPEFULLY I GET SOME ANSWERS