I'm sure that someone else will do this better than I - there may even be a guide around somewhere. But here it goes....
There is some stuff in the manual about C&C. It took me a couple of readings - it's a little scattered.
Basically, your units need "orders" to: (1) set a movement objective (2) to move somewhere other than in the direction of the objective (3) to change stance defend/advance (4) to call in arty. The lead squad from each platoon will gain orders each turn if they are not suppressed. Those orders can be used by any of the squads in that platoon if they are in contact with their platoon leader and not too supressed themselves.
Orders gained by the A0 unit will be shared with the units below it. (If you have a company commander, they may also be gaining and sharing orders.) That means if your squad uses up it's platoon leader's orders, it may be able to access orders from the A0 unit. Two special units - the CP and HQ - also gain orders and share them with units in their vicinity (five hexes?).
The number of orders a unit gains or can carry over from turn to turn is determined by it's rank - I think there is also a little table of this in the manual. Most regular units can only carry over 3 orders per turn, though your A0 unit may carry over as many as five. You plattoon leaders loose all their accumulated orders if they are forced to route or retreat. You can see how many orders a unit has available, and who they are coming from, when you select it and look at the info panel at the bottom of the screen.
The number of orders it takes to do something can vary depending on whether the unit is in "direct" contact with it's platoon leader (usually means within 3 hexes, though some elite commanding units seem to have influences that extend further than that.) There is a little chart in the manual that breaks down orders costs. Some quick ones: 3 orders to set a movement objective, 1 order to move outside of objective if the unit is in direct contact - 3 orders if it is in radio contact, one order to change stance (advance/defend) of a single unit if in contact - 2 or 3? if in radio contact, 3 orders to chance the stance for the entire platoon.
To change the stance of a unit, open the unit's info panel (select it and space-bar) and look towards the bottom on the left side - near where range, etc. is. You can click on stance to cycle it between advance/defend. When you do this with the platoon leader, there is another switch that will apply the stance change to only the current unit or to the whole platoon - default is only the current unit.
Some things that C&C will teach you: (1) notice which of your units doesn't have a radio - they will be stranded if they stray too far from their commander. (2) Choose your objectives carefully - if you run out of orders you can't move. (3) Defensive stance can make a big difference now - less likely to retreat when fired upon, more likely to take op fire, more likely to find cover. (4) Protect your command units - they aren't just undergunned squads anymore. Keep them close to their squads so that they can rally them better and won't have to spend as many orders to make a quick course correction. (5) Be careful with your FO - they can't call unlimited arty anymore or they run out of orders. Keep them near your A0 so they will always be in contact and have it's orders to use.
I hope you like it. I used to complain about C&C, but once I got the hang of it I found it really enhanced game play. I think it's a must for the megacamps.
I'm sure there are some mistakes or omissions in what I've written - hope other readers can offer some comments.