Use layers to keep different objects on separate layers and edit them as a group (hide, adjust their transparency, lock etc.). Layers can be found by clicking the two stacked diamond symbols in the top menu bar.
A. Rename layer: Click on the layer name to rename it
B. Opacity: The eye icon will hide or show whatever is on the layer. Move the white circle to adjust the opacity of the layer between 1 and 100%
D. Add layer: Click to create a new layer
C. Lock: Select to lock the layer
Swipe left on a layer to reveal more options for that layer (F and G below)
F. Duplicate layer: select to duplicate the layer. The copied layer will be named the previous layer with -Copy at the end
G. Delete layer: Select to delete the layer