Each unit has a specific movement allowance and so many shots per turn. So if you use up all your available shots during your move then you will not have any left over for oportunity fire. I saw another posting initially saying there was no fog of war. There is 3 possible settings for spotting and accuracy. Suppression results in loss of available op fire and even movement.
Suppression directly affects moral.
If a units moral is low enough it will rout, retreat, or even surrender. Delays in orders for bombardments. Most games last from 10 to 20 turns. Engineers can blow up bridges. The manual mentions barges for inf.