What do you want to know about it? Generally speaking, it's a 'cloud storage' service, which means that all the files you store on there are on a server somewhere that's owned by Google, and you can access them from anywhere in the world (that has internet access). The advantage of this is that they're safe if something bad happens to your home computer and you can't get at the files on it (so it's a good backup facility), and it's useful if you often need to use the same document in different places. For example, I use a similar cloud storage, Dropbox, for my uni work - if I write something in the uni library on my laptop, and save it to Dropbox, when I go home and use my main desktop PC, I can access the same file and edit it without faffing around with a memory stick or emailing it to myself.
It's also good if you need different people to have access to the same master document to make changes and collaborate; I don't know how Google Drive specifically does this but most of these services have a way to invite certain people to access a specific file (while the rest of your documents remain private) and either only read or edit if you want them to.
Does that help? If you need more specifics I think you need to ask more specific questions....