If you're still in college/university, enrol in an undergraduate introductory physics course. If you don't have time for that, go to the library and borrow what

If you're still in college/university, enrol in an undergraduate introductory physics course. If you don't have time for that, go to the library and borrow whatever text book it is they use for those courses. Alternately, just browse the physics department shelves in the library and read whatever book catches your fancy.