Question 499456
Generally, it means to show your work.  Each teacher is a little different, but unless you are doing a formal proof, then you don't need to use words (most of the time) to justify each step.  If you are told to foil (2x-1)(2x+2) showing all work, then you would right out each step:
4x^2+4x-2x-2
=4x^2+2x-2
If you were told to prove that the product of (2x-1) and (2x+2) is 4x^2+2x-2, then you would need to justify each step by using some type of theorem, property, postulate, etc.
Generally, all that is required is for you to show your work so that someone can follow how you got from point A to point B and say ok, they multiplied here and then moved this over to the other side...