A floyd rose is a floating bridge, meaning that the bridge is not fixed on the body of the guitar.
The bridge "floats" between two opposite tensions. The strings pulls to one side and the springs to the opposite side. Both must have the correct tension for the bridge to float correctly. If you see a floyd rose or other floating bridge sick inside the body of a guitar, that means the tension of the springs is too high. If the bridge sticks out of the body, then it's the string tension that is high.
The wammy bar is a lever that helps you to move the bridge. This makes for interesting pitch changes as you are changing the tension of the strings by pulling or pushing on the bar.
Most floating bridge will come with locking nut on the headstock. Since you are playing with the string tension, locking the strings in place will insure the guitar doesn't go out of tune.
It's a tricky beast :)
