The "civics book" version of US government says that the judicial branch does not make laws. Instead, it simply interprets them. However, this view oversimplifies what the judicial branch does.
In truth, the judicial branch does make law whenever it decides a case. For example, up until a few weeks ago, it was not clear whether the Commerce Clause would allow the federal government to require people to buy health insurance. In other words, we did not know exactly what that clause really "said." Now we know that (according to the Supreme Court) the Commerce Clause does not allow the federal government to give such an order.
In this way, every time the Court makes a decision, it is telling us exactly what a law means in a given situation. By doing so, it is participating in the process of making law.