Hi,
It would take too long to explain it all here.
You first need to do some basic tests with a simple adc routine using a 10k pot as the input source, so you understand how it works, then the answer for you keypad should become clear.
Have a look at that Winpicprog ADC tutorial which gives a good description of the software.
However his extra ADC input hardware is not needed for a simple voltage test, just feed the 10k pots slider directly to the adc pin.
Also see this sites ADC lesson
**broken link removed**