It depends on whether you are solving for x or for y. Whatever variable you are solving for you want to isolate it on one side. Unless you know the values for x or y, you will have an answer with one of the variables in it. For example, to solve for x:
2x-3y=10; first move the 3y to the other side so, 2x= 3y + 10- you have to add 3y to cancel it from a negative (-3y). Then, you have to get rid of the 2 multiplied (next to the x). Since it's multiplication, you'll have to divide.
Remember a key rule: whatever you do to one side, you have to do to the other. So, divide the 2x by 2 and then divide 3y + 10 by 2. The 2 will be cancelled by the x and your answer will have to remain x = 3y + 10 divided by 2/ The answers stays this way because you do not know the value of y to do any more.
Hope this helps!