In Civil War Commander, you are a Brigidier General for either the Union or the Confederate army. You have command of 5 regiments consisting of infantry companies, artillery batteries, and cavalry troops.
Your mission is to hold 5 sectors of terrian either by defending or capturing them. How you deploy your given troops, how you use your reserves, and the abilities of your regimental commanders will determine the outcome.
Win and you'll be a hero and may be promoted. Lose and you may be removed from command. Such is the life of a CIVIL WAR COMMANDER.

(From Publishers Website)

In short, the game represents one battle. Players draw for who will be the defender for the battle. The defending player plays 2 unit cards per terrain feature and keeps a 5 company reserve. The attacking player plays 3 cards per terrain sector and keeps a 5 card reserve. After an initial round of combat, both players commit their reserves for the second round. At the end of the second round, whichever player controls 3 of the 5 terrain sectors in play, is the winner.

Units include infantry companies, artillery batteries, and cavalry troops. The units stat's vary depending on the units assigned combat value and how that type unit is effected by the terrain being fought over.

There is also a campaign version with the player gets points for each victory for a set number of battles. The player with the most points at the end of the series of battles, is the campaign winner.