This is the default view which appears whenever you select an assembly and open the Part List Manager window.

All assemblies and sub assemblies appear on the left with the sub assemblies directly beneath and slightly offset to the right indicating that they're 'inside' the assembly directly above.

The list to the right always shows the components contained within whichever assembly is currently highlighted in yellow.

If we clicked our 'CA1001-1' sub assembly on the left then the window would instantly change as shown on the following page.