Well, stick around long enough and you'll learn everything about us xD
Let's see... Furries, for the most part, are just people who are fans of the Anthropomorphic style of art... That is, art that has both human and animal characteristics. Common examples from Disney would be the beast from Beauty and the Beast, Robin Hood, as well as The Lion King, and more recently, Alpha and Omega. There are several other examples. A TV show currently on Cartoon Network called Regular Show features several anthropomorphic creatures.
Many furries will take on "Fursona's" which are simply furry characters, much like a D&D character... You'll often see artwork of peoples fursona, and fursuiters will almost always use their fursona as a template for their suit. While on sites such as this one, most of us use this persona rather then our actual information, as a fun way to interact with each other.
I can't think of anything else right now, but if there's anything in particular you'd like to know about, I or someone else would be happy to explain. As for your question "What it is and why people do it", for me personally, I love the artwork, and, being a heavy player of D&D, as well as other similar games, I'm all for having a character and interacting with others via that character. Again, that's for me personally.
Well, the artwork and the fursona's brought me here, but I'll be around for a long time because I've met some great people and made some close friends. I haven't been here long, but there are some really great people who are furry, on this website in particular. I'm assuming your boyfriend is one of those people