I've had horrible luck and wasted tons of money on low quality weight gainers, so you definitely get what you pay for. I've switched over to higher quality like BSN's Syntha-6 and Tru-Mass, which put on weight for me. Ultimate Nutrition's Muscle Juice 2544 was a complete waste for me.
At night, I take 3 scoops of Tru-Mass with 1 tablespoon of canola oil, some peanut butter, all in water, but you could use milk.
During the day, I use two scoops Syntha6 in about a tablespoon of egg whites and the rest water, but again you would try milk. This post workout and some other time (like between breakfast and lunch)
But the other guys are right, solid meals is a must. For breakfast, I use Cottage Cheese with Mandarin Oranges, Vanilla Yogurt and chocolate milk. Protein bars throughout the day, chicken and rice for lunch, tuna fish on wheat for mid-day snack, and chicken and potatos for dinner. That's 4 real meals, couple bars and 3 shakes so it gets expensive.
At 16, you merely have to feed your body the nutrients and just a little direction in the gym, meaning you don't have to do 24 sets for biceps because just 8 sets will do. I see young kids do Incline Bench, Flat Bench, Decline bench, dumbell flyes, machine flyes, pec decks...etc etc etc... which I think is too much for chest.
Ok, I'm off on a tangent... in the gym do compound movements like Squat, Deadlifts, Bench, Military press, then do smaller muscle groups after. You'll be adding pounds in weeks
