I learned by my dad teaching me, reading on forums, and by pulling things apart - sure, it hasn't worked out the best all the time, and it's cost me and my parents a little more money than I would have liked, but in the end you learn from it, and it's a great experience when you finally understand how to do something reasonably complex. After a while you start to pick up the terms, and understand what they mean. And for the things you don't, you can always do a google search. Most of the information you'll readily find on the internet is pretty much correct, but keep your common sense about you and you won't end up doing anything to your car that you will regret!
The fact that you know how to do an oil change means you're off to a good start. Just keep an ear and an eye out, try and do some more maintenance on your cars, and if something seems simple enough to pull apart, then go ahead, and try to work out how the part works, then put it back together. Although, don't attempt this if you only have one car and it's your daily driver!
www.howstuffworks.com is an amazing site for learning the basics of how an engine works. Once you understand the theory behind that you can start to learn the more complicated things, and because you then understand how an engine works, the more complicated things will make more sense!