If the water isn't flushing:
There is likely something blocking your pipes; you'll need to unclog the pipe using a plunger. Simply push your plunger into place and move it up and down rapidly to dislodge the debris from the pipe. Don't flush your toilet during this process; once the clog has moved, the water should drain on its own.
Nothing happens when I flush:
If your toilet handle doesn't seem to be flushing, lift the lid on the back of the tank and check that the handle is still attached to the flush mechanism. There should be a small chain linking the two.