Creatine helps the ATP cycle when you're lifting. Conventional wisdom says that when you 'load' creatine, IE take it for a week in moderate doses, with servings immediately preceding work outs, it allows you to push harder, and longer due to more efficient energy conversion and stores in your muscles.
This has been my experience as the conventional wisdom suggests. As for weight gainer, you really need to be burning 1k of calories in your work outs for it to be really effective in my opinion. Otherwise you just get 'fat'. Some people say that dextrose (sugar) helps protein absorption, which I believe to be true. However most weight gainers have a disproportionately high amount of dextrose in them. The GNC generic stuff is exceedingly bad in this regards. If you're concerned with your body composition you would probably be better of going with a low sugar whey protein, with a good amount of Casein protein and other slow burning long chain proteins. I swear by Isopure, but others are good as well (it mixes clear in water). You can also just get pure whey, which I believe something like On Whey is good for.
Mixing creatine in with your protein shakes also helps. For the 'sugar' you're best off using fruits as they don't instantly metabolize and get burned up immediately. You DO need some sugar to most efficiently absorb protein in my opinion.
Also, don't overdo the protein especially if you haven't ever taken tons of it. You'll give yourself the 'protein farts' and your bowls won't be happy with you. I find anything more than 50-60g or so of protein after a work out to be largely wasted.
Some people 'think' that more than 35g of protein at a time is just wasted, but different people's physiology can process different amounts of protein. My own experience seems to suggest that more than 50-60g for myself ends up coming out in the stool straight through. Anything below that is fine for me. But your mileage may vary. Also, after a workout you can process/absorb significantly more protein within the first hour after a work out. Something to keep in mind.
Things to keep in mind:
Creatine creates water bloat. You will retain more water, but this is good for bulking, and building muscle. You NEED TO DRINK LOTS OF WATER. I tend to drink a gallon + a day on Creatine to make sure my liver doesn't hate me when I'm 40. Creatine Mono-hydrate can end up being bad for your liver in high concentrations, so moderation, lots of water, and not doing it for longer than say 6 weeks at a time is recommended.
Pre-Workout nutrition is just as important as Post-Workout nutrition if you're trying to gain muscle. You don't want to cannibalize muscle trying to get energy to work out. So feed your muscles before and after the work out with adequate protein and complex sugars from fruits preferably.
Banana's are my favorite because the potassium keeps me from cramping up post workout, but that's just me. Berries, and other fruits like pineapple are good too.
At night, most people swear by cottage cheese as it keeps you full and you don't wake up hungry. Also consuming a bit of protein before you hit the sack gives your body building blocks to build muscle while you sleep, and keeps you from cannibalizing muscle overnight.
For ultimate muscle build out, make sure every meal has a good portion of protein, and eat 2-3 snacks in between, with protein. Food bar's high in protein, and other things are good to have handy in between meals.
All that said, you need 1.5-2g of protein per pound of muscle mass, to adequately feed your muscle gains.
Last but not least, don't over train. If you are still sore from your last work out, don't work out that muscle group again until it is mostly not sore. You don't have to wait until it's completely NOT SORE, but your muscles are telling you they need time to rebuild, and recoup. Otherwise you are just destroying muscle as opposed to building it. High repetition weight lifting is also bad in this regards. If you can do more than ~15 reps, you have too little weight, and it's an aerobic exercise, not anaerobic, which encourages atrophy (muscle's getting bigger).
Ok, these are some of the basic building blocks you can start with. I'm not a personal trainer, nor am I a professional body builder. This is just what I've learned from my foray into building a better body.
There are many other things you can do to step it up another level, but you have to get the basics right first. Things like BCAA's (branch chain amino acids) help increase recovery speed, and muscle mass quicker, but cost more than just plain ole' creatine and whey protein. For your money, working hard, eating properly, and feeding your muscles gets your furthest from the get go.
Others may tell you differently, but learn what's working for you first, then add on to it later.
p.s. one thing to note: don't take creatine with coke or anything acidic as it neutralizes the creatine. It works most effectively with just water. Some people supplement dextrose with it to help increase the absorption.