Hi Colleen,
Its primary purpose is to provide emergency communications. It doesn't get much press, but it is a great service to the community. For example, here in the southern states we have to face the threat of hurricanes. While many of the storms we face each year are relatively weak, some can be absolutely devastating. Such storms can render all forms of communication around the city and outside the affected area out of service. Telephones, internet, cellular service, and even radio communications used by emergence services like law enforcement, fire, and EMS can all be taken out of commission. This is where ham radio comes in. Many amateur operators primarily operate for the purpose of providing such service. Many have portable stations with battery power, generators, portable antennas which can easily be set up, and regularly practice passing emergency traffic under various simulated situations. Such stations prepare themselves for relaying vital communications on behalf of their community when all other forms of communications are down. As was stated before, ham radio covers a lot of distance, so not only can it relay communications around the affected area, but can also reach out for help to the rest of the world when no other form of communication is available.
That said, it is a hobby and it's most often enjoyed recreationally. Many people experiment with building ether own radio equipment; some enjoy experimenting with new ways to transmit data using radio; and others just enjoy contacting new people or just keeping in touch with their friends or family over the radio. There's really something for everybody in the amateur radio hobby. It's a fun hobby and very educational. There is always something new to learn. For me, there has always been a certain magic I can't explain when I transmit a radio signal and am heard by a station on the other side of the world on my own personal equipment using absolutely no internet or other aide whatsoever - just radio waves. While I do understand a little bit about the technical aspects of how radio works, it's still this magic that keeps me coming back for more!
73 (radio slang for "Best wishes")
Danielle