"Frequency" means how often something happens. When you say how many times it happens every SECOND, you can call the number Hertz, or Hz.
In the graph, there are 10 vibrations in 10 seconds, 20 of them in 20 seconds, and 30 in 30 seconds. This should pretty much shout at you "THERE'S ONE VIBRATION EVERY SECOND !". When you realize that, you can say the frequency of the vibration is 1 Hz.
The graph tells us nothing about the speed of the waves. I suspect there's another picture to the question that you didn't include. If the other part shows the wavelength, then we could figure out the speed. But with just what you're showing us, we can't.
