Theories are organized sets of hypotheses, organized sets of whys laid out in an attempt to understand some group of facts that have been observed. In scientific terms at least, theories have stronger support and explanatory power than laws. Good theories are testable, they can be shown to be wrong, or if we are
And, in scientific terms at least, "law" doesn't mean quite the same thing as in everyday speech. In everyday speech, laws are rules we are supposed to obey - things we have to do but sometimes don't or things we get in trouble for doing. By contrast, in scientific terminology laws are descriptions of things that happen. They are primarily observatory in nature, meaning they tell us what happens under a certain set of circumstances. Apple rolls off head, apple falls. It tells us the what of what happened. But - and here's a crucial part - it doesn't tell us the why, and that's because we generally don't understand why they happened, we just know that they do. So in terms of evidence and explanatory power, theories are the better bet.
However, in the spirit of internet memes, let me pass on for you a PSA recently forwarded to me about a law you should follow.
Because seatbelts? Not just a good idea. The LAW.

