Commanding in the field

Stand near your army and press the command key: select units, move them, form them up, and fight.

Inner Council & Guild Leader KeysGLeft MouseRight Mouse

When you are within 300 m of one of your guild's armies, its card bar appears at the top of the screen. Press G to enter command mode: the cursor frees and you can still walk. Press it again to leave. The Overhead button on the card bar switches to a commander's view.

Left Mouse a soldier
Select their unit. Drag a box to select several.
Ctrl + click
Add to the selection. Clicking cards on the bar selects too.
Right Mouse the ground
Move the selection there.
Right Mouse drag
Move there and set the front: the drag sets the width and facing of the line.
Right Mouse an enemy player
Attack them.

Orders on the card bar

GroupButtons
MovementCharge, Hold, Follow me, Advance, Fall back, Retreat, Army orders (resume its standing orders)
FormationLine, Loose, Shield Wall, Square, Wedge, Column
MissilesFire at will, Hold fire

If G says no army of yours is near enough to hear you, get within 300 m of it.