Your privacy
Some things have to run for the site to work at all — keeping you signed in, remembering where you are in the program. Beyond that, nothing runs unless you say so. There is no advertising or analytics on this site today, and none will start without your agreement. Full detail is in the privacy policy and the terms.
Keeps you signed in, remembers your place in the program, and keeps the site secure. The site cannot work without these, so they cannot be switched off.
Remembers small things you would not want to set twice - a chat conversation you have open, a panel you collapsed.
Counts which lessons and handouts get opened, so the program can be improved. Never used to identify you.
Would let advertising platforms know you visited. Nothing of this kind runs today, and it stays off unless you turn it on.