Good Advice from Bio Nerd; here are some specifics.
Determine your 10, 5 and 3 rep Maxes on Bench Press, Weighted Dips, Overhead Presses, Squats, DeadLifts and Leg Presses, Bent Rows, and Pullups/Weighted Pullups.
If you haven't been lifting for more than 2 months (in order to gain size, you can combine one exercise for each body part and do 2 warmup sets of 12 and 4 "working" sets of 5-8 reps every other day. Make sure you are consuming a MINIMUM of 10xyour desired bodyweight in CLEAN calories
45% complex carbs, 35% lean protein, 20% healthy fats. Don't forget at least 100oz of water each day to keep your kidneys flushed of excess protein!
I gained 20lbs in 3 months this way.
I put on another 15 pounds (of LEAN MUSCLE) in the next 13 weeks months by adding Barbell Curls, Preacher Curls, Close Grip Bench Press, and HEAVY Tricep Pushdowns as an arm day; then i did 3 additional days of Shoulders/Chest, Back and Legs. I did at least 3 sets of Ab work at the end of each workout, working each body part (or set) every 5 to 7 days.
Hope these specifics help!