how to setup I/O port in AT91SAM256

 how to setup I/O port in AT91SAM256

I am really interested in embedded area. I am just a beginner.
I bought a AT91SAM256 kit by PNlab at VietNam. I read a lot of books, but i have some confuse about:
+ All I/O (Input/Output) pins of this kit are defaulted an Input. If I want to setup pin PA7 (PIO7) is a output pin, I must configure this pin. Inversely, if i choose this pin is a kind of input pin, i don't care about to setup.
+ I design an external circuit. The output of this circuit will be an input of the AT91SAM256 (such as PIO8). Therefore, I want to be sure that this pin is a kind of input pin. How do you do that?

Thanks in advance.