What does .aspx mean?

Ok. I know a lot about web desinging and all, but I'm not 100% sure what .aspx means, or what it does. Any help?

Please give me as much details as possible.

How can a teenager make money online?

OK. I'm 16 years old, and I have a few hours after school that I can work for a website. (And weekends) Until a few weeks ago I ran a website for someone and I only charged him about $20 a month. A...