Use your mouse or finger to change the pitch and volume.
Starting off, I found the simplest way to generate sound in a sketch, which is by playing a sample. By loading in a sample of a sine wave, I could then use the mouse's x and y positions to influence the pitch and volume!
Simply setting the pitch required more thought than anticipated. You see, we can only use the p5.js function sample.rate(s), which causes the sample to be played back at s times the regular speed. To find the frequency of the resultant wave, we must multiply this rate by the frequency of our wave sample (sf) which is 1000Hz in this case. Thus, to play a desired frequency f we must set the rate to f/sf.
A final nuance to mention: the map from x position to frequency is linear. However, there is an exponential relationship between frequency and pitch; doubling a frequency always increases the pitch by an octave! Explore this listening to a small frequency change at a low frequency, vs the same change at a high frequency.