On screen notes are notes that everyone can see and use in “real time”. Meaning whatever you type on there, everyone can see it. You don’t know who is actually typing though, so if you’re the host and you don’t want players to use it, then this can be disabled in the host options menu. On the bottom right of your screen, there will be a button icon with a red circle in it. Click it to activate it and begin typing in the new window that pops up.
You can write anything in here, which can be good for keeping track of certain things in games or calling out people, whatever you’d like to do. BB Code can also be used, which can bring an extra element of fun to the game.