What does frequency determine for sound waves?
Frequency is the number of cycles per second.
In sound, this corresponds to an increase in pitch. This increase is perceived as a higher tone of sound, like a smoke alarm.
Below is a link to an online tone generator and you may compare different frequencies. (I suggest you try it)
Frequencies are measured in Hz (hertz). A hertz is a number that represents the number of waves per second. For example 500 Hz means 500 cycles (waves) per second and 20000 Hz means that there are 20000 cycles per second.
To summarize, an increase in sound frequency corresponds to a perceived higher pitch sound. A high pitch sound is like a mosquito buzz. A low pitched sound is like a tuba (a low frequency that has a small amount of cycles per second).