What causes a turn to end?
In single player your turn ends when all of your units are out of movement points or when you click on the turn button at the bottom right side of the HUD.
How can I tell what units still need to move during the turn?
Hitting tab will cycle through units with movement points left.
How do I split an army back into its constituent units?
Select your group of units, and you should see an icon for each one on the HUD. If you click on an individual icon, you can separate that unit from the group by hitting the eject arrow that appears above the icon, or by simply right-clicking away from the group in the direction you'd like the unit to leave.
Why do I only have two buildings to build in my one city... what do I need to do or achieve to get more?
That could be several different things(here's a few possibilities): you may lack the resources(gildar, materials, food) or level requirements to build grayed out buildings, or if you lack a range of even grayed out building options you may need to research further into the tech trees to unlock more building options.
Why does my army not attack the obvious enemy on the screen?
Have you declared war on this enemy already? Have you possibly made a non-aggression pact with them? Could be a turn issue if that unit is out of movement points for the current turn.
Is it possible to talk to a unit that has been combined into an army?
That depends on who you're trying to talk to... enemy faction or wondering champion?
