To play the drums well, you need to be able to place any kind of note on or in between any beat with any limb independently from the parts played by the other limbs. A good way to start developing this ability is to play a basic beat and then vary one of the parts.
The following examples should help you become confident with varying your snare drum parts. First try example 35 which uses only the right and left hands. There is no count written beneath this example, but you should know the system well enough by now to count the snare drum hits louder than the hi-hats.
Now try the following examples which make use of the right and left hands along with the right foot. When you are comfortable with these, try making up some variations of your own.