A single noteboard constitutes a single piece of laminated Legal-sized piece of paper.
You get 5 of them spiral bound together. They are double sided but I believe the first has instructions on it so you effectively get 9 sides to work with.
Personally I had to ask for one 'refill'.
You have to have used up the noteboards before getting another one, so if you are down to half a page, I would raise my hand and signal to the proctor that I need a new one. In case they are helping someone else, you have half a sheet to work with before it fills up.
You can save a bit of time by raising your hand and motioning in some way that you want a new noteboard.
You can't really 'erase' on the noteboards, but if you get a single digit wrong it is quite easy to smudge it with your finger. Otherwise, its better to just start over.
Good luck with your upcoming test!