Here's a quick answer.
Creatine is used by your muscles to create energy, ATP. There are two other ways your body can create energy (aerboic and anaerboic) using glucose, but creatine is by far the fastest. When it comes to strength training, it's extremely helpful. The more energy your muscles have, the more weight/reps you can lift, and the bigger your muscles will get.
Creatine's effective because your muscles are not at full creatine storage capacity. Thus, the additional creatine you consume fills that void.
If you discontinue it, nothing detrimental will happen. You may lose some strength and stamina, but nothing as far as health risks.
If you can stick with the powder. It's a lot cheaper. You can get 3 months worth for under $20. It's tasteless. You can add it to water, and you won't even taste it (it'll just have a sandy feel).
Don't let people convince you that you need a special creatine. Creatine monohydrate is fine. The Journal of the International Society of Sports Nutrition just released a report not too long ago that claims "all creatines are created equal thus far." So, don't spend $40 on a creatine product. Plus, creatine ethyl ester tastes horrible.
Start with a loading dose, around 20 grams per day split into 4 doses, for 3-5 days, and then take 5 grams prior to your workout and 5 grams after your workout.
Many people will tell you to drink plenty of water while taking it to avoid muscle cramps. It's a good idea, but it's never been proven to work.
You really have nothing to worry about. It has the most scientific evidence behind it, and it's one of the safest dietary supplements on the market. Clinicians have even been studying it in the elderly.
Muscle Geeks: Mixing pharmacists, trainers, and fighters