[john.gersh]

The pencil icon indicates the active layer. What you draw goes into this layer. The box indicates the layer(s) containing the currently selected item(s). If the selection is in the active layer, the box shows up around the pencil.

It's a little confusing because of the different ways to change things in the canvas panel:

Here "layer" means the layer item as shown in the Canvases panel.

The highlighted layer in the Canvases panel is selected; it's the one to which layer actions are directed. For example, hitting delete deletes the highlighted layer; new layers are created just above the highlighted layer. Change the selection by the usual methods for selecting items in a list: clicking, using arrow keys to move up and down, shift- or command- clicking for multiple selection.

The pencil indicates the active layer. This is the one that you're currently drawing in. You change this by clicking on the layer to the left of the layer thumbnail, where the pencil will appear. This also selects that layer. (Clicking other parts of the layer selects but doesn't make active.)

The box(es) indicate the layer(s) containing the current selection in the drawing. You change this by the usual selection actions in the drawing.

And then there's the little stack indicating a shared layer. I don't think that can be changed.

The layer properties icons (visible, print, lock) show up when you hover over the layer and can be changed by clicking them. That click does not select the layer.

Clear?