Usually, the use of creatine is split into a loading and maintenance phase. During the loading phase, large quantities of creatine monohydrate are taken. Because the creatine only slowly disappears from the body, a maintenance phase in which less creatine is taken will still provide the body with adequate levels of creatine. For suggested duration of the phases and quantities see below.

It is recommended to drink lots of water while on the creatine.

[From the Training-Nutrition faq: Powder form is preferred over capsules.
Most users recommend a loading phase when first starting with CM. For 5 to 7 days, take a teaspoon (approx. 5 grams) 5 times per day. After that go on maintenance at 5 grams twice per day.]

Note: it is discouraged to use caffeine while on creatine; while creatine makes your muscles hold water, caffeine will do the opposite, thereby reducing the effects of the creatine intake.

Don't mix creatine with citrus juice. Orange, grapefruit, cranberry, in fact, most fruit juices have been most recently found to neutralize the activity of creatine monohydrate. The reason is the waste product creatinine develops. A lot of you put creatine on your tongue and drink it down with grapefruit juice. If you have taken creatine this way in the past, stop it now! You are not getting creatine, you're getting waste product.

Do mix creatine monohydrate with warm water--in a glass. This is the only way to ensure you're getting the full benefits of creatine in its dry form. Creatine does not have to dissolve to be effective.

Do be sure to drink a full eight ounce glass of good water 8 times a day. Creatine pulls water from other parts of the body to perform its work in cell volumization of the muscle. This is what makes the muscle larger and firmer. Replenish your H2O!

To actually answer your question. As soon as you load up on creatine your muscles will fill with more water leading to a size increase. I really notice it in my biceps. The moment you stop with the creatine this water goes away.

What creatine does is help you perform additional sets quicker by replenishing short term muscular energy stores faster. Will this make you bigger fo' real? Maybe.

You need to eat more. Lots o protien. I'm a scrawny little fucker too, I feel full very easily. Just gotta force the food in. On the bright side, should you decide to diet off some fat at some point it might be easier for you than most folks.