The Workspaces. You use the arrow keys to change / navigate around it. You use the Super key + S to invoke it.
Why 4 workspaces? Why not 2? Why not 6? Will Ubuntu allow further configuration with regard to workspaces? The Window Overview. You invoke it by typing Super key + W.
This overview should help the user spot the focused window right away. Perhaps by greying out the unfocused windows? Putting titles over the windows will help in identification.