If you can find an older laptop, or some other computer that you can utterly destroy without having major consequences, then you're set.
What I did to learn about computers was meddling with the configuration. Go to the Control Panel, find out what each icon and option does.
Questions? Google them.
Need more answers? Post your questions in a forum.
Find out how to change your screen resolution, your desktop image, how to create new windows users, set their passwords.
Find out gradually how your computer actually connects to the internet (like, is your router's password WEP or WPA?)
If you have LOTS of time and are really willing to learn, try installing a Linux distribution (Linux is like Windows, but totally free and a little harder to use). Linux and its huge community are very likely to teach you all you need to know about computers, one step at a time :D