EDIT: lol i didnt see that you are 14. uhh ya wait about 2 years then follow my post. at 14 your body is still not at point of rebuilding muscle. all that you will get from you lifting weight, is tired.
the keys to lifting weights for the purpose of getting bigger are knowing when to stop lifting, and knowing when and what to eat.
before starting out make sure you chose a weight where you can do 3 sets of 8-10 reps, where you struggle to get those last 4-5 reps of your last set up. its more important to choose a weight that you can get all the reps done than having a heavy weight.
cycle days in which you lift. Heres what we used in football.
Monday, upper body (bench, incline, military, traps, curls and such)
Tuesday, lower body (squat, dead lift, power cleans, hams and quads)
Wednesday, cardio. this is key because you want to let the anareobic muscles to have time to recover. the way muscles get bigger is that during a workout, muscles tear. the two day recovery time allows your body to rebuild the muscle stronger and bigger than before. that is when you get bigger.
Thurday, upper body
Friday, lower body
saturday, cardio.
sunday, SLEEP! lol
my football team had a whole nutritional course we had to follow. and man did it work. i dropped 10% body fat. the main keys are to drink lots of water throughout the day. i was at about a gallon of water a day. also, gatorade AFTER workouts, not during or before. and from the end of your workout, you have about 30 minutes to get the protein in you. with that not being much time, what you can do is take a protein shake before working out. that will extend the time frame a little. after lifting empty about 2 cans of tuna on 4 sandwiches. wheat bread, and a little mustard to hide the god awefull taste of tuna. make sure you have 3 good meals a day, along with fruits and vegetables (this will provide the sugars your body will need. so 2-3 eggs or even a bowl of cereal. then the tuna for luch, and some turkey or chicken with rice for dinner. And finally, i think it goes without saying, no soda. nothing sugary (cept the fruit and veggies). and most important of all, NOTHING FRIED.
Hope this helps you as much as it helped me.