Hey, I'm almost 16 and I've been lifting for a while so I tihnk I can help you. I agree that you should stick with compound excersizes (using multiple muscle groups) for at least a few weeks. Get some general exercises in (bench, parallel squat, dead lift, dumbbell curl) for 3 sets of 12 with aobut 1 minute and 30 second break inbetween at first.
After a while, you might want to do some research on lifting.
For instance, right now I'm building mass, and I have a 3 day split for my workout, and I'm lifting everyday a different set of muscles and take a break every 6 days. For mass, I'm doing 5 sets of 8 or 10 with a little less than 1 minute break inbetween each set. This is a hypertrophy workout. You need to eat quite a bit to gain mass at first. Afterwards, when you've gained enough, or after about 2 months or so, you can start "cutting" where you trim off the fat by diet and some cardio.
I'm not sure what exactly you need to know, so reply with your questions