Yeah this game could have used a day to smooth out the kinks, let me explain.
The goal is to make the results wave (on the rights) identical to the target wave (on the left) the difference wave on the middle should go flag. Note letters and numbers work like on a piano so letters go C, C#, up to B, and numbers go from 0 to 8, do the lowest note you can produce is C0 and highest is B8, that gives you 108 possible frequencies for each wave.
Volume simply changes amplitude of each wave that adds up to the results. You have actually 5 different waves: sine, triangle, square, saw and noise wave, and each on later levels add up to the result wave.
Special simply adds a skew to each wave, changes their sound slightly.
The gamę does require some time to get a feel for each setting, which is why each level adds one wave