Chess Openings

Hello there!

I am a novice player and currently learning opening theory.

I am currently studying a book called Essential Chess Openings by Speelman and Keene to improve my opening repatoir, but there are so many and so many different variations of each system that it is difficult to take it all in, let alone find the time to study them all.

What I would like to know is: do I need to learn all openings to help improve my game or just certain ones such as the Ruy Lopez and Sicilian? And is learning them  ad-hock from a book the best way to go about it?

Glyn.