First of all, I’ve got to commend you for being so pro-active. The fact that you have the desire to learn this stuff, on your own, and to ask questions, speaks volumes. There are a few things that come to mind here.
Find anything you can related to environments & props. Jump into your favorite game, like Skyrim, and find something in the game that makes you go, “that is amazing!” Take a few screen captures, jump out of the game, and reproduce it. Do this over-and-over again to build your skill and portfolio. If you’re feeling extra adventurous, expand on it in some way.
If something truly has you stuck, find a dedicated forum filled with artists, and ask them how you can get the same look/feel/etc. Ask many more questions… even the ‘stupid’ ones.
Show your work off where your fellow artists hang out. You want to engage with them as much as possible to get critiqued.
Find an independent developer who is looking for environmental / prop work. Offer to help!
You’re not doing anything wrong right now. Nobody wants to hire someone without evidence that they can do what they say they can do… so your best ally will be your portfolio. If you come close to graduating High School, and still don’t have the portfolio/confidence, find a great school. Spend even more time building up that portfolio, while being around similar people. After a year or so, hunt for an internship to get an even accelerated ‘real world’ experience.
Stay motivated and keep creating. You can totally do it.