There are lots of tutorials, but most of them cover only the basics or obvious functions.
But basically layers works like layers in other image editor tools.
The bottom layers cover the top ones.
The clone tool has a small video tutorial when you mouse hover the button.
Select a layer, right click a point to mark the start point.
Select other layer or stay in the same.
Left click and draw to copy the pixels from the initial point. Keep the mouse button pressed while drawing.
Was this helpful?