how to put a layer below my working layer as a reference?
It just doesn't work, when I erase something in one layer it erases from both
edited April 2018
It sounds like you're working with tiles and they're mapped, if that's the case, you have to unmap the tile you want to use as reference layer. Hover over the "tile placer tool" icon to see how. Usually it's cmd+right-click on mac and ctrl+right-click on windows