Lemme try.
Remember those weird virtual pets people had on key chains or something like that? I think they were called Gigapets or something like that. You had to train and take care of them.
Somewhere about 3 years ago, someone decided to create a virtual world for pets. They don't look as stupid as gigapets (that I remember) but they've simply gone way too far. I mean that in a positive sense. You can buy food and toys for your pets, build a house, battle other neopets, paint your neopets different colors and styles, etc. You simply can't keep up with all the changes.
But here's the important thing. You pay for everything in Neopia with neopoints. You get those by playing games; the score you get translates into neopoints, depending on the difficulty of the game and other factors. You can also sell stuff you acquire or play the Neopian stock market.
One more thing. Unlike gigapets and all it's inceptions, you don't have to clean up your neopets doo-doo and your neopet can't be killed. I've tried. So if you get disinterested and come back six months later, no big loss. Your pet will be awfully hungry but no hungrier than if you left him for a week. (He'll even say he's dying, but it's not true)