I'm new to this generator, so I'm not sure how a lot of it works. Specifically, the "Size" area of "Generate." I've tried inputing numbers, and it doesn't seem to be doing anything to the map. The map I'm trying to make just isn't working for my campaign, and I wanted to redo it, which is why I'm trying to figure it out. Could someone help me?

To make the "size" work you need to type in you value (in "cells", e.g. 100) there and press Enter while the cursor is in that input field. More info here: link.