Well you haven't given any specifics here. Are you looking to do this in a programming language? If so, which one? Or are you looking to do this from a shell?
The best documentation that I've found for doing this in C is from the kernel documentation itself:
Documentation/gpio.txt. If I remember right, you must first request a GPIO pin (
gpio_request()), then set its direction (
gpio_direction_input() or
gpio_direction_output()). If you want to send output, then you can just use
gpio_set_value(). If you want to receive input when the state changes, you can map the GPIO to an IRQ number (
gpio_to_irq()) and use that number with
request_irq() to set a handler. Finally, remember to call
gpio_free() to release the GPIO pin.
You may also find
this documentation to be a good reference, but it relies heavily on the sys filesystem rather than on the kernel API, so I'd suggest only using it to test GPIO access from a shell rather than in an actual program.