OU812
That's just limb independence and it is tough to develop. All you can do is play slow until you get the hang of it. So often times when doing a basic fill on the drum set you will be playing 1/8th notes on the snare/toms and 1/4tr notes on the bass. So on a table top or whatever play an 1/8th note fill (1 and 2 and 3 and 4 and). At the same time tap your foot to only the 1/4tr notes (1 2 3 4). This should help you build the limb independence you need.

Riseagainst Drummer
It basically independence between the upper and lower part of your body. For me, different foot and hand playing came naturally, for others it may not and that's completely fine. Although, when i started drumming (4 years ago) i was most certainly not as good as i am now with out of sync beats between my hands and feet, but with practice and 2 lessons... i learned how to get better at it.

David
Limb independence and coordination is all about starting slow and using a metronome.