How do you play chords that are like c/b or b/g and things like this. Is there a way to know what to play, or do they need to be memorized? If so where can i find what they are?
C/B means that you play a C chord with B in the bass. B/G is B with G in the bass.

When I say bass, I mean that it's the lowest note of the chord on the guitar. The note is not always played on the bass guitar.
   C  C/B   G  G/B


They're called slash chords.