You use their currency - "Gold", in order to buy clothes and other shit. First day signing up, you are a poor avatar with starter clothes and 200 gold, which isn't worth shit. As you progress, you earn more, buy more, and do more fun stuff. They have a ton of items to select from. The possiblities for your avatar are endless.
However, this site is full of noobs, Narutards and furfags. Noobs usually spend their time trying to find dates and having virtual sex with other noobs' avatars. And if you are a teenager who likes slipknot and other nu-metal bands, DO NOT go to the Metal forums. It is full of elitist assholes and faggots who only like bands that nobody has heard of. They will flame you. This is the unfriendly side of the website.
Despite that, this website is a great website and is, in a way, better than fucking myspace.
Now it's slowly becoming a pay-to-play website. The newest scam is "Free" Gaia Cash offers that wind up getting a ton of viruses on your computer, or dozens of telemarketers calling your house every day.
The site has interactive worlds known as Towns or Rally where many users get together with their avatars and hang out. Other worlds are usually sponsor based worlds, like MTV Hollywood Crap world.
They used to have this really cool feature called Gaia Cinemas where we can watch funny old ass educational videos with other avatars, but they tossed all that completely.
This website has become increasingly boring. Nobody goes on here anymore except Asians and 12 year old white girls. Items are way to damn expensive to work toward them anymore. This site has pretty much lost all it's former glory and become a giant cesspool of watery diarrhea.