So far you have learnt about basic rhythm in the "Basic Rhythm" section. If not, then learn the parts in that section before you move on to here.
Rhythm can be as complex as lead or soloing on the guitar, it just depends on how far you want to take it. Some people seem to think there is a difference between a lead guitarist and a rhythm guitarist and that you can only do one or the other in a band. To be good at rhythm you have to know a little about scales around the chords. And to be good at soloing or improvisation you have to have a good understanding of chord positioning and have natural rhythm.
By calling yourself a lead or rhythm guitarist you are selling yourself short, your should simply be a guitarist and be equally as good at both.