Pick a tool and draw. Hover a line of yours to grab it — drag an end to reshape, the middle to move, N to describe it, Delete to remove.
Your drawings are labelled with your name so we can tell whose reasoning is whose later. Both are stored in this browser only, and asked once.
Checked before you are let in — a wrong key would mean nothing you draw is saved or seen by the other person.
Anything you leave empty stays empty — skip is fine. What matters most are the two lines at the bottom.