In scientific discussion:

A theory is a working model, backed by experimentation, of the way the universe works in some way or another. Some examples of theories you have probably interacted with (or at least know of) are Darwin's Theory of Evolution, Newton's Theory of Gravity, and Einstein's Theory of Relativity.

These all work to explain a phenomena to the best of our knowledge, but they do have their limitations. Newtonian mechanics, for instance, breaks down in cases of extreme speed or extreme gravity, and Relativity exists to deal with those cases - Relativity meanwhile breaks down at very small values, which is where Quantum Theory comes in to fill in the gaps.

A hypothesis is your educated guess as to the outcome of an experiment before you run it. A really oversimplified example is "if I drop this feather and this bowling ball from the same height at the same time, I hypothesize that the bowling ball will hit the ground first" - then you test that hypothesis by running an experiment, and see if the shape of your intuition is right. In that case it is, but if you were to say something like "I hypothesize that if I drop a bowling ball and a basket ball from the same height at the same time, the bowling ball will hit the ground first" and then tested it, you'd find that it wasn't true, or at least wasn't as true as you thought it might be.

The real culprit isn't weight/mass, but air resistance. If you take that ball and feather and put them into a sealed chamber that you then vacuum seal, then drop them, they will fall at the same rate.

Making the hypothesis helps to narrow down the possibility space of a weird phenomenon, and get to those theories that you want.