The basic rock beat is 4/4, so you count 1-2-3-4. And to create the rock rhythm, you have to place the emphasis on the off-beats, which 2 and 4. So it goes like this: one, TWO, three, FOUR. At least that I was taught.
But I personally think this rhythm exist in basically kinds of music. I listen to hip-hop, R&B and pop music and this beat, which is considered a defining characteristic of rock'n'roll, is there. Why is it called ''the rock beat'' then?