How to create a redstone clock.
A redstone clock is an easy mechanism to make that powers pistons, dispensers, etc repetitively.
Redstone clocks are simple to create and are used for more then you think they can be used for, in other words, a lot of things that you may or may not know.
You should learn how to create one by watching this one minute and thirty five minute tutorial even if you aren't trying to make one.