After logon, a hierarchical tree view is shown to the left of all screens.
To maximise the area taken by the main display pane you can hide the tree view by clicking once on the thin vertical bar that separates it from the main pane.
You can also adjust the size of the tree view display area by dragging the thin vertical bar to the desired position.
If you do not see the tree view displayed, it is because it is hidden. It can be restored by dragging or clicking once on the thin vertical bar, which will be at the far left-hand side of your screen.