Why no other replies?
K, you need to plan your own routine, whatever suits you. By this routine I mean, what body part(s) you're gonna hit at the gym on which day of the week; this keeps you accountable too. There're some excellent workout logs on the forums that I suggest you check out. You can't afford to hit the same body part, for instance your arms(biceps/triceps) daily or do a full-body intense workout daily cos you'll over work your muscles and they won't be able to keep up with the regeneration. Its recommended to rest a specific body part 1 - 2 days after a workout so the muscles can grow back stronger. While you're resting, you can do other stuff; when I'm resting my arms and shoulders I like to chuck in some cardio and core/abdominal work. Anyway, your body will tell you when something needs its rest, when you first start off, you'll definitely feel sore the next couple of days.
As for the gym, I suggest learning to use all the equipment and figuring out what works what muscle. From there workout with 8 - 10 reps during each exercise for about 3 sets. The reps and sets vary among ppl so you should be able to figure out what suits you better than I do
As for diet, I'm pretty much a noob in that area.... but you need to keep your calories high, I'm 15 and I eat 4 - 5 meals a day, about 1000 kcals per meal. Most ppl recommend 5 - 6 small meals a day. Your body needs the energy to rebuild and expend during workouts. Protein goes without saying; nuts, soy milk, beans, lentils, avocados, I find myself eating a lot of broccoli too o.O
Most importantly, have fun! (I'm half-asleep as I type this so anyone please correct me if anything I said came out wrong)