C.U.N.T said:
Inside joke....
Anyway, perform a search. This may sound like a simple question but it's actually very vague with an involved answer that is probably larger in scope than you're anticipating. In other words, it would be difficult and time consuming to try to answer it for you right here.
If you want the most general answer I can give:
-Eat much more than you currently are with an emphasis on high-proetin foods.
-Eat smaller meals, more often during the day. Never go several hours without eating high-protein food.
-Stick to heavy, basic, free-weight exercises like the squat, bench press or incline press, deadlift, dips, chin-ups, bent-over rows, straight bar curls, skull crushers, stiff-leg deadlifts, military presses, etc.
-Rest and sleep as much as you can.
-Drink lots of water.
-Be intense and focused while in the gym, but don't spend over 1 hour training.
-Train to failure.
-Choose a weight that allows you to reach failure around 6-10 reps for each set.
Best of luck bro.