A couple things that threw me at first...well, actually for awhile until some benevolent posters here cured my ignorance of the obvious and helped me see the light.
Look at the Action buttons very carefully when dealing with the chain of command. Some of them only become clickable when certain conditions are met, and it is easy to blow past them...took me a long time to figure out that creating a division took an eligible leader, the money and supplies available to pay for the privilege, AND using that little join action button when you have a leader and an eligible unit or units BOTH selected by CTRL clicking. I think to be eligible the leader has to be active and unlocked, the unit(s) have to be unlocked, and you have to recite the second verse of "Dixie's Land" while you do all this (OK, I made that up. Any period song will do).
Another item that threw me was Railroad repair. Perhaps it's my slanted view of the world and obeying orders that the Marine Corps has given me, but I was a little surprised to find out that if you order a unit to perform the Repair Railroad action, and it fails to accomplish the mission, next turn the unit will assume that the failure to perform said mission has earned it the right to take two weeks of rest and relaxation unless you click the action button again.
Roger, I'm not the brightest crayon in the box, but with the help of the kind folks at the forums here and at Matrix, I'm getting more comfortable with AACW. There is a lot going on in the game, there was (and is, I'm sure) a lot of info that somehow slipped by me at first, but the game is more than worth the learning curve.