How does the UK Visa biometrics thing work?

I know I have to make an appointment online, pay, attend and all this, I'm just wondering what exactly happens after I have it done. Do I have to lodge my application then and there at the biometrics office? Or do they give me a form or something that I then send in with my application at a later date? If it's the latter, how long does it remain valid for? The best I can find online is that they keep my information for 10 years, I highly doubt that makes it valid for 10 years though. I'm a tad confused with this and it probably doesn't make much sense but if anyone can help me out it will be highly appreciated.