You must upload a black and white image mask of the map you wish to add walls to. The floor should be solid white, while the walls should be solid black. After you have uploaded your image and tweaked your wall settings, click 'Generate Walls' to create the walls (this can take some time). Once it's done generating, the preview image should show your image mask with coloured lines overlaid on it to represent the walls. You can select a polygon index to change certain things about each wall polygon individually, like the wall type or whether the polygon is closed or open. Or you can edit them all at once. Once you're satisfied with your walls, click 'Download' to download the occluder definitions xml file. Certain settings like Wall Contraction, Inaccuracy, and Pixel Offset don't update in real-time and require the walls to be regenerated manually to take effect.