A Guide to Civil War Research.
There are 3 pieces of information you will need to start your research.
The Name of your ancestor
The State where they served
Their Unit of service
For each engagement in the war there is an "Order of Battle" showing which troops were involved and their chain of command. Generally these are much better documented for the Union troops and the Confederate opposing forces are only recently being pieced together by researchers, particularly for the late battles in Georgia, South Carolina and North Carolina.
Generally speaking, regiments moved and fought together throughout the war, so when tracing the actions of an individual, you should focus on the movements of his regiment. Sometimes, but not often, a lower level account will be found, such as a diary or a set of letters by a member of the regiment.
Once research is exhausted on a particular regiment, look to the "sister" regiments which served under the same Brigadier General as a brigade. Within this group you will almost always find some first hand accounts.
The next step up in research is to look for memoirs of the Colonel of the regiment(s) or the Brigadier General who served over the regiment. These higher level first hand accounts will have good battle descriptions and casualty counts, but seldom mention individual men by name unless they were officers or distinguished themselves in service.
Finally look for higher level histories of the various battles and campaigns. Most of these were written more recently and have few individual details, but serve to give a broader view of the war.
This set of OnLine lessons is excerpted from our "Guide to Civil War Research" books. We have specific volumes for some states and a general volume which will help you research other states.