there are no buttons for the co. the uav is not working anymore and you cant choose multiple teams.
the only really important note:
while selecting a sqd and pressing the normal voice button, you can talk to every specific sqd. with pressing "v" your a talking to all sqds at the same time (same as in vanilla).
the most useful job a CO can do is to bring the sqds doing something specific and the only tool PR hands him for this job is his voice. that means you have to pray to your sqds which can become pretty fast annoying cause many SLs dont like COs telling them something to do and they just ignore you. because you have no authority you cant do anything against this.
in the rare case the team is talking to you, this could be a good example how a good Co will work (without any buttons):
you see 1sqd requesting helitrans, your helisqd is busy so you are telling this squad to move meanwhile to a plain insertion point. suddenly this sqd reports tank inc, you are withdrawing the choppers from the hot zone and you are ordering instead the tanksqd to this position. while sq1 gives you intel on the enemy tank you can pass this to your tanksqd to bring them in comfortable positions. and so on and so on ... its all about communication and informtion flow, no buttons
so, the position "Commander" is a misunderstanding, he cant command in any way. he can just be a tactical advisor or a supporter. as supporter a CO can be very effective but its far away from this what a guy that is called "COMMANDER" is supposed to do.
in my opinion the reason why 95% of all games are running without CO.