Rudiments are the drummers equivalent to playing scales. The point of rudiments is to allow you easy access to the kit, i.e. to stop you wrapping your arms up in a knot and instead, make things look effortless.
Here are the basic rudiments: (L=left hand R=Right hand)
1. Single stroke roll: R L R L R L R L
2. Double stroke roll: R R L L R R L L
3. Paradiddle: R L R R L R L L
4. Double-Paradiddle: R L R L R R L R L R L L
5. Paradiddle-diddle: R L R R L L R L R R L L
It is a good idea to practice these with a metronome at many different tempos. Ideally on JUST the snare drum at first to save you getting distracted. Later, once a good amount of control has been achieved you will apply these to the drum kit. I found that practicing them on a pillow really helped me improve my grip and technique, this is because there is very little or no "bounce" from a pillow... the energy you put into the stroke needs to be pulled back out by you and this will help when it comes to playing on toms that have far less bounce (especially low toms) than the snare drum.