When you register, Facebook automatically assigns you to the not-super-useful Global network, which gives you access to globally organized groups and events. But you definitely want to join at least one more network. Technically, you can belong to as many as five different networks, but if you're like most people, two or three (a regional network plus a network for your work, school, or both) fills the bill. Anyone can join a regional network (like the one for Denver, CO, for example), but you have to have a company-issued email address to join a company's network, and a school-issued email address to join a school's network.
For security reasons, you can't join multiple regional networks (meaning, you can't tell Facebook you live both in Phoenix and Miami) and you can't switch networks every two minutes, either. In fact, Facebook limits you to two changes per network per two-month period—and if you actually change that often, your account may be flagged by Facebook's fraud-sniffers. So when you choose a network, make sure it's the one you really want.
To join a network:
At the top of any Facebook screen, click the down arrow next to Networks.
In the drop-down list that appears, click "Join a Network".
You can't just join any old network—you have to have a valid email address that matches the workplace, college, or high school network you want ...