To dither means to add noise to our audio signal. Yes, we add noise on purpose, and it is a good thing
We add noise to make a trade. We trade a little low-level hiss for a big reduction in distortion. It's a good trade, and one that our ears like.
Whether it's 24 bits or 32 bits, we have to find some way to move the important information contained in the lower (least significant) bits into the upper 16 bits for recording to the CD standard.
It turns out the best solution for maintaining the resolution of digital audio is to calculate random numbers and add a different random number to every sample. Then, cut it off at 16 bits. The random numbers must also be different for left and right samples, or else stereo separation will be compromised.