Making this a sticky.
Depends on your age. You in college? Lots of colleges have backpacking and camping clubs that you can enjoy. If youre still young i can recommend boyscouts, but that may be too much BS for what you just want to learn.
Backpacking magazine has an excellent 101 list thats worth a look...http://www.backpacker.com/backpacking101
Here's a little of what to expect on a trip: http://www.journeywest.com/WB/pages/gettingstarted1.html
And another one: http://www.backpacking.net/beginner.html
Theres a lot more out there if you spend some time to surf google.
Main things to keep in mind are to stay in shape, use common sense(which is a rarity these days), and be prepared. You dont need all that super featherweight gear like all those bigtime hikers have. Just a good tent, boots, sleeping bag,knife and pack. Everything else you can pretty much make or slowly acquire. Gonna warn you though, most backpacking gear is $$$$ unless you go the milsurp route.