The operators on this panel are explained from left to right, top to bottom.
This will bake all the masks on the current layer. Once clicked there will be a popup that allows you to replace all the current masks on the layer with the mask after baking. This is helpful when using generator masks that are computationally expensive.
This will hide all the masks on the active layer.
This will delete all the masks on the active layer.
This will allow you to add a mask to the mask stack.