These commands are all various shortcuts that can be used by players to facilitate the selecting of units by a variety of ways.

Left Click: Select unit
Double Left Click: Select all units of this type on screen
Left Click on nothing: Deselect all units
Left Click and drag: Select all units in this box
     * If your selection is primarily mobile units, only the mobile units will be selected. The game will also guess which type of unit you meant.

1: Select all units in Group 1
Ctrl + 1: Set selected units as Group 1
Shift + 1: Add group 1 to your selection
Shift + Ctrl + 1: Select the factories in Group 1
     * All 10 number keys work for making/selecting groups.
     * Units can belong to multiple groups.
     * Your groups will appear as icons on the right side of the screen.
     * When selecting a group, factories will not be selected by default.
     * Factories give their group numbers to units they build.

Shift + click on unit icon: Add idle engineer to this group

Ctrl + X: Select all units and buildings
Ctrl + A: Select all air units
Ctrl + S: Select all sea units
Ctrl + L: Select all land units
Ctrl + B: Select all engineers and the Commander
Ctrl + Z: Select all units of this type on the map

Ctrl + C: Select all units and buildings on screen
Ctrl + Period: Select all engineers on screen
Ctrl + H: Select all factories on screen

Comma: Go to Commander
Alt + Comma: Select Commander

Period: Go to nearest idle engineer
Alt + Period: Select nearest idle engineer
Shift + Period: Cycle through idle engineers

H: Select nearest factory
Ctrl + Shift + L: Select nearest land factory
Ctrl + Shift + A: Select nearest air factory
Ctrl + Shift + S: Select nearest naval factory