This menu facilitates working on subcircuits in hierarchical schematics.
Hierarchy → Up (Shift-H U) allows you to return to the toplevel schematic of the subcircuit or symbol you’re working on if you went into it using the one of the menu items Hierarchy → Down Schematic or Hierarchy → Down Symbol, correspondingly.
Hierarchy → Down Schematic (Shift-H D) opens the subcircuit schematic for a selected component, of course, if it has one.
Hierarchy → Down Symbol (Shift-H S) opens a selected symbol for editing its contents. Unlike the previous menu item, it goes into the symbol file, not into its subcircuit schematic.