Easy answer, glorified squad leader with access to fire support.

Primary Responsibilities:
Coordinate communication.
Call in fire support.

Secondary Responsibilities:
Use your binoculars to observe things and report them.

Ternary Responsibilities:
Kill things with your sub-machine gun.

ONLY YOU CAN PLACE TEAM WIDE MARKERS.

REPEAT THAT WITH ME, ONLY YOU CAN PLACE TEAM WIDE MARKERS.

The markers on the map you place are visible to everyone on the map. EVERYONE.

Talk with squad leaders to determine enemy troop concentrations, then place artillery markers( number 6 key while map is open) and let the people on arty know you need them to fire on that position. They will be able to see the range and will hopefully comply.

Pro tip: A good commander will "coerce" 1-2 players to play artillery at the start of the game. 3-4 artillery players may be ideal if you posses superior resources and/or need a breakthrough.

Additionally, talk with commanders and place your observe marker to let everyone know where enemy armor is located.

Lastly, you may want to divide squads between defending the current objective and attacking the next. Realistically, they may or may not listen.

Two types of supports a commander can call in, each cost a different resources.

Manpower Supports:

Last Stand:
You do not lose resources for a short period. Useful if the enemy is making a push or you are spending resources on other support types.

Reinforcements:
Your men are worth more while defending objectives. I recommend using when you have some men in an objective and the enemy is half way to capturing it. This will let your men hold on longer and may allow reinforcements to reach them.

Improve Morale(Or Whatever they renamed it to)
Use this if you require more of the resource from the objective you are about to capture. Otherwise this is useless. I don't use this often myself.

Munition Supports:

Bomber:
Call in a bomber. It performs a bombing run with the center of the bombing run being the marker. The line is approximately 200 meters long. Will DESTROY TANKS, SANDBAGS, AT...etc. Takes approximately 45 seconds to arrive after being called. Therefore, NOT GOOD on moving tanks. Left click the icon before you call in to CHANGE THE DIRECTION of the strike.


CAS(Close Air Support/Fighter):
Call in a fighter to perform a strafing run. Works against infantry. VERY SMALL WIDTH(<5 meters). Most place directly on enemy or it will miss. Attack line is approximately 200 meters long with center on icon you place. Does not work against tanks or most static placements.

Supplies:
Super cheap at 15 munitions. It drops 100 resources on the marker after approximately 30 seconds + 30 second crate descent => 60 seconds.

This can allow your squad leaders or YOU to build garrisons on the location. Additionally, it can allow others to build AT, sandbags, etc. Communicate with squads leaders and set up garrisons where needed.

You are NOT part of a squad. You can respawn at garrisons. Your fire supports should be saved until they provide actual value and they must often be used quickly. Therefore, you should not be putting yourself in the thick of battle very often. Stay alive and stay 200-300 meters behind the front lines.

Try to think tactically.

Advise squads to flank the enemy.

Ask if they need AT, supplies, bomber runs, etc.

Let allies know when you advance or need to retreat.

Show confidence.

Direct tanks.

Direct artillery.

And may God help you, because this guide sure as hell didn't.