Before taking paintbrush in hand and adding color to everything in sight, one must begin with the first steps.
Most of us start out in miniature war gaming because of our love of history. Sometimes it is a particular battle or a famous general who catches our imagination. Once we are intrigued, we absorb every bit of information we can.
There are a wealth of information and resources available on the American Civil War. It's a good idea to start out simple and basic. This way you do not feel overwhelmed.
Research a particular battle and go from there. Most times you will find a smaller engagement That is part of the larger battle that you can focus on.
Once you have picked your battle It is time to figure out the "Who, What, Where, Why, and How" of the battle.
Who fought this particular action? The commanders involved, the units and the troop strengths.
What did they fight with? What equipment was involved? This basically asks what did the armies present at this battle use as far as equipment. This question also helps with your representation of the models on the game table. The uniforms they wore and such.
Where did they fight? This is self explanatory. This involves looking at maps and reading first hand accounts of the battle and battlefield. This part goes into modeling the battlefield.
Why? Basically, Why did the parties involved fight this particular battle? Did they just happen to run into each other accidentally? This question will usually go along with the rules that will be played for the battle.
How? Some examples of How are. How did the battle end? How many soldiers/ units where involved? How long did the battle take? How the heck am I going to do this?!? ;)
All you have to do is start small. Pick a small part of the overall battle and do the research to answer the questions. Once you have the information you can begin to collect the models necessary to represent your army.