One of the regulars on this board will probably break everything down for you, so I'll just drop you a few tips of advice and let them take it away:
1. Creatine probably doesn't come in 21 gram servings (man, that would be a monster size bottle though!) It's usually recommended 5grams per serving of creatine (unless you are one of the 300lbs guys on here).
2. I personally would never buy anything from GNC, I think I may have once a very long time ago. They want you to become a member of their club in order to get discounts, when the discount price is usually what you'd pay in any other store without buying a membership. I know it's annoying, but shopping around works best, in my opinion. I always shop around. I have about 4 stores that I like a lot, but not every one has every product I have, and some sell certain things cheaper. Here's what to look for in creatine. a) you want a creatine monohydrate (there are a few other crappy creatines out there like creatine phosphate, and unless you like crapping out 80% of your supplements, I don't recommend them) b) if you can get it for a cheap enough price I'd highly recommend a "micronized" creatine monohydrate. I've tried regular, and micronized and the difference has been significant for me. c) you want to buy a reputable brand. I have no idea what GNC's rep is for the purity of their products, but I don't recall hearing anything outstanding about them. I use Interactive Nutrition (but that's a Canadian brand). I've used Pro Lab's creatine. It was good, and cheap. I've used Champion Nutrition and there's was good (although mine was premixed with glucose, and not dextrose, I was a little dissapointed with that). Some of the guys on here can recommend some other good american brands.
3. Buy some dextrose to mix with your creatine. It helps transport the creatine through your digestive system in to your bloodstream and hence your muscles much more effectively. You can buy a bag of it at most health stores, and even a lot of grocery stores. It looks like a kilo of cocaine though.
I'd recommend mixing 5 grams of creatine with 50 grams of dextrose in to just plain water, or water with something for flavoring. You could also just throw your creatine in to a bottle of frutopia (it mixes very well with fruitopia) but remember to drink a big gulp before you throw your creatine in, or it will spill at the top.
4. As for protein, it all depends, again, I wouldn't recommend a GNC brand. There are just so many better ones out there. The guys on here could probably name 10 better brand names. I'd take their recommendations and shop around for the best deal out of the list. As for servings, it depends, some proteins offer 20 grams of protein per serving, some offer up to 50. The ones I use are usually around the 30 gram size. Let's be real though, you can make them anything you want, I mean just use two scoops and you have 60, ya know? or use a half and you have 15. For your age and size, I'd say 20-30 per serving is plenty. Try to buy a Whey Isolate when you get your protein, so you don't get ripped off with some GNC Chalkboard scrappings. Isolates mix better and are used better by your body.
5. As far as when to use, or in comparison with real, whole foods. Use common sense, don't drink protein drinks INSTEAD of eating. Use them when you can't eat, or when it's more convinient. Obviously cooking chicken breasts 5-6 times a day isn't realistic. Figure out what works best for you, but I think most on here would agree that you should take in protein at least 5 times daily, spread out and for your size you should try to get 30 grams of it per time. So if you ate 30 grams of protein for breakfast, then had a protein shake 2.5-3 hours later, then ate lunch a couple hours after that, with 30 grams of protein in it, then had a protein shake 2.5 hours later, then had another 30 grams in your dinner, and another shake 2.5 hours later, you'd be doing fine.