When I joined the ServerFault community 18 months ago I thought I was a pretty kick-arse system administrator. Turns out I wasn't, I was actually pretty average.
Virtually everything that I've learnt between now and then has been through just reading things on this site, and researching whatever I need to in order to answer them. It's been a great way to put myself into scenarios I hadn't dealt with in the past and forcing myself to swim. And on the occasions when I've got it wrong, the community here has been helpful in pointing it out.
Also, you if you come across concepts you don't understand, or need help with, we're generally pretty good at answering them just as long as you're not a tool about it. If you explain your question and what you THINK the answer is and where you're stuck, we'll help.
Seriously, this place is a great place to learn. Just read other peoples questions. There are a lot of beginner, basic questions. A great place to start is Evan's epic Subnetting explanation, and a great one from yesterday was a question about how the internet actually works.