Most rock songs you will encounter will mainly employ the use of powerchords. They are really easy to learn.

Standard E, Eb, C#, and whole step powerchords:

A--3--5--7--2--4
E--1--3--5--0--2

Basically what you are doing is either fretting 2 odd or 2 even frets, but they have to be the next odd/even fret down the line (i.e. 1 and 3, but not 1 and 5) or it sounds like junk.

For dropped D tuning and B, G#, C#, F#, A#, b tuning its different. The strings must be fretted all on the same fret, i.e. fret the first 3 strings at 2 and it will be a powerchord.