If you press ''Shift``-button at using drag and drop, the element will be copied. Without pressing ''Shift`` button the element will be moved.
Double-click in the layertree will be zoom to the selected object.
If you are selecting some special layers, you can adjust if they are painted more in the foreground / background by setting the ''Z-order`` in the lower left corner. Also the opacity is adjustable in some cases, which enables you to see (partly) through that layer.
The following lists the typical content of the layer tree: