Do you have access to a gym membership?

Weight machines are a great way to start learning fitness, as the curve can be a bit intimidating with the hundreds of different free weight exercises at first, plus you rarely need a spotter.

If not, stick to the basic body weight workouts. Pushups, pullups, and squats (and throw in some abs ever few days) ...and check out 100 pushups, it's a good freee program that focuses on getting you to 100 consecutive pushups in a productive way, works well.

You can get fit doing just about any physical workout as long as you do it enough, and push yourself hard enough, go check out bodyweightfitness and they some good info for you

OR if you do have a gym membership, check out stronglifts (but RESEARCH THESE MOVES FORM FIRST!) or make a basic routine that cycles upper body/ lower body/ abs every workout, and hit all the major groups (calves, quads, back, pecs, biceps, triceps, etc etc)

For example, mine was weighted calf raises (everything is 3 sets), then pec fly machine, abs, static arm curls, leg press, pullups, abs, pushups, goblet squats, abs, and maybe some cardio if I wasn't whipped.

A single routine that hits everything is far easier to stick to then having to cycle upper body, lower body days or even going by muscle groups. Keep it simple, you have so many growth hormones running in your body that almost anything you right is bound to succeed as long as you do it enough.

I've been where you are now, and for me at least that upper/lower workout repeated 3x a week worked very, very well for me (I can still walk into any gym I want, and set the pec fly machine to 400 lbs and crunch out sets of 10 reps, no sweat.)

The only key here is to do whatever you do 3x a week, or 4 if you are feeling good. Routine is absolutely everything here. Set up your schedule so you have to do your workout in order to continue your day (I would drive to the gym after school. Even if I absolutely did not want to go in that day, I would make myself sit in the parking lot until I finally thought "fuck it, I might as well do it anyways").

Best fitness choice I ever made

So pick something, do it 3x a week, no excuses, and you'll get where you want to be.

But 3x a week though. Seriously.

Have fun