That's a good, simple description of a "hypothesis".
Another way to describe it is "an educated guess".
Once you have it in words, it's time to start checking it out, with experiments that can show whether it's true or not.
If your experiments seem to show that your hypothesis seems to be true, that doesn't 'prove' it, but you can start calling your hypothesis a "theory".
(It's possible that you may never be able to 'prove' it. It may remain a theory forever. Like gravity, germs, atoms, and relativity. Thousands of successful experiments don't 'prove' a theory, but it can be trashed by one good, valid experiment to show that it's false.)