Hello, Joanna ---

I don't see an example problem, but will try to make one up.

Suppose you want to combine like terms of the following string:

      (2x + 3) + (x -3y +7) - (2x + 4y - 6)

First, remove the parentheses by distributing the + and - signs across the second and third terms:

     2x + 3    + x -3y +7      -2x -4y + 6

Now bring the x-terms together, then the y-terms and then the number terms:

    2x + x - 2x      - 3y - 4y       + 3 + 7 + 6

Add all of the x-terms, the y-terms and the numbers:

          x - 7y + 16

This would be your final answer. 

These problems can be much more complicated, but this is the general idea.

Good luck!