You multiply or divide, depending on what is contained in the equation. But if there is addition or subtraction in the equation as well, then you do that too. But the order you do it in all depends on how the equation is written, what you're solving for, whether there are parentheses or not, and if there are, where they are placed.
If there's a particular problem you're stuck on that involves multiplication/division, feel free to post it or pm me about it and I'll try to help out.