Long story short, CMB is your grapple modifier and CMD is your defence against. Since it's not really that long of a story:
CMB - Combat Manoeuvre Bonus
(BAB + Str + Size)
Your Combat Manoeuvre Bonus is very similar to what your grapple modifier did for you before, except that it applies to all Combat Manoeuvres, which include all those many-odd things that few people ever remembered existed (Trip, Sunder, Overrun, etc.). Essentially, it is so that you don't have to go look up what modifiers you apply to a Trip attack or a Sunder attack, they're all in one place.
Special: Tiny or smaller creatures us Dex, not Str. Also, Monks gain ability that lets them pretend they have a Good BAB when doing manoeuvres, making them a bad idea to grapple with.
CMD - Combat Manoeuvre Defence
(BAB + Str + Dex + Size + Some of the modifiers that apply to AC)
This is basically your AC against Combat Manoeuvres. Various things that apply to your AC (insight bonuses, deflection bonuses) also enhance your CMD. Unlike CMD, Tiny and smaller creatures don't get to substitute out their Str. I can't think of anything else to say for this.
For a complete list of Combat Manoeuvres,
click here. It should be pretty much everything in the special attacks section from before.