How does creatine work?

You'll usually gain water weight on it, due to your muscles being fuller. Your muscles are two types of fibers, slow twitch and fast twitch. Slow twitch uses glucose (sugar/carbs) to fire, and fast twitch is fired with creatine. Slow twitch is used for endurance activities (like marathon running) and fast twitch is used for, say, lifting heavy weights up. You normally get creatine from meat, your body needs meat to synthesize it. So it'll help if you're lifting weights seriously, or otherwise have a high high training volume, but for a normal person, not really. Even for most people, if you've got high meat intake, you probably are getting enough creatine anyway. HOWEVER, if you're vegan/vegetarian, supplementary creatine can be helpful.