Can you elaborate on texture slots, the Accumulate option, and Alpha Erase?

posted to: 2D Painting

I'm coming from GIMP/Krita where we have "layers" and can go back and change things and also have an Erase brush. The forums say Erase Alpha is the same as Eraser, but I don't think I fully understand what it is doing since the paint data is still there if you Add Alpha back. It seems to me Erase Alpha is adding alpha layer and Add Alpha is taking away Alpha layer so I feel like I'm missing something fundamental here. Since it isn't erasing the actual paint "layer" but replacing it with Alpha,  I lose my background UV grid. The Blender manual mentions the Accumulate option, but doesn't give much detail or a use case. You mention using multiple texture "slots" but I haven't yet heard when we should use those. Of the three, which is closest to the Eraser brush and "layers" - and can you briefly give examples of when we should use accumulate or multiple texture slots?