it's like a laser printer but instead of toner it uses gooey resin. project (in UV light) a shape on the bottom of the goop and it will start to solidify in that shape (once it touches oxygen)... so gently pulling some solid surface goop out gets you to the point where you can "print" stuff! Pretty cool! It's not clear to me if the resin solidifies only on contact with UV light and the oxygen level is controlled from below or above, but at any rate the balance of UV light (in a particular projected design) and oxygen is what makes this possible.
I think the oxygen prevents solidification which is what stops the object from sticking to the screen they project the image on to. By the looks of it the oxygen just diffuses from the air through the screen.
First carefully consider what you want to print. For example, this resin type printer is not a great technology for creating strong replacement parts around the house.
