[wh-uws]

First off exactly like folz and others have said. Make something. BUILD SOMETHING as people often call it. It can be as simple as you want.

Make sure to avoid feeling inferior with whatever it is however it comes out. ALOT of programming is learning by doing. Don't get caught up in well "all I did was x". You can still learn alot from actually having done x that can help you when you eventually want to make y.

Next its good that you are getting started early.

I wish I had the foresight to ask this question of a community like HN (much less known about/ had HN) back in high school especially so I could have gotten started working on subjects like the ones you can read here

http://www.quora.com/What-does-it-take-to-become-a-programme...

I've been learning programming since about middle school (about to graduate from college now) and I'm still learning everyday. People well into their careers from CEOs to new hires will tell you the same.

Dive into something, start small and scale up. You'll be amazed at what you can come up with given time.