You could start by reading up on microcontrollers in general - and PICs in particular. Here are some possibilities:
http://www.rentron.com/books.htm

Some free ones here:
http://www.mikroe.com/en/books/

And most importantly, visit the PIC manufacturer's website to download datasheets, app notes, etc.:
http://www.microchip.com/stellent/id...PAGE&nodeId=69