I take it that you've just begun, or about to start your PPL nav training.
Just read through your PPL study book, whether it be the Bob Tait one, or the 7 ATC PPL/CPL books. Those explain the theory required sufficiently.
In terms of advice, these threads should contain everything you need:
http://www.pprune.org/dg-p-general-a...-visually.html
http://www.pprune.org/dg-p-general-a...does-work.html
PPL navigation is pretty straight forward, you'll do fine. Any hassles or queries please ask, but the above threads are quite handy.