From what I recall, its an encoder. You have 12 address bits, which you can select. Consider that like your "password". And then you parrallel load your data to the 8 data pins, and then when you active the transmission enable pin (i think it was active low), it will serially output your data in its new encoded format out of Dout. That would then go to your RF module.
On the receiver side, you need to make sure that you have the same "password" selected. So, make sure that your address's match for both transmitter and receiver and you should get your originally data out (it could be backwards tho, not too sure).