The conventional answer here is that the legislative branch makes the laws. For the United States as a whole, that means that Congress makes the law. For each state, it is the legislature that does this. For local governments, it is typically the city council (or some other name that means the same thing). At any rate, it is the legislative branch that makes laws -- that is the very definition of a legislative banch.
A more sophisticated answer would take into account the fact that all branches of government participate in making the law. When the executive branch decides how to enforce the law it is, in effect, making law. For example, the Congress may have decided what the speed limit on the freeway is, but it is actually the police officer who decides what it truly is because they are the ones who decide if you're getting a ticket.
The judiciary makes law in a similar way -- we don't know what the Constitution really says, for example, until the Supreme Court tells us.
So there are at least a couple ways to answer this -- the conventional and the more complex.