In your own words, explain how the frequency of an ocean wave determines the motion of a surfer on the wave?

As the frequency increases the wavelength decreases

We have a basic equation in oscillation which says that frequencies and wavelength are inversely proportional to each other. As the frequency increases the wavelength decreases so when the frequency of the waves increases the height and depth of the waves changes hence the surfer will be more likely to fall. On the other hand if the frequency is low then the wavelength will be high therefore the surfer will ride smoothly.