In the early stages of tracing your family back in time, the pension records from the Civil War are a important document. If your relative served in all likely hood they applied for a pension record. It does not mean that they got one, but even a rejected application can have a great deal of information.
Here again the more information and details you have on the solider the better. The information provided on the service record application is the same for the pension record. The information is a first hand account by your ancestor or widow on the events that occurred during the individuals service. The primary information is person's name, date of enlistment, location of enlistment, birth date, location of birth, injuries during battle, death date if widow and location of death. Another important item is a list of where they have lived since the war and complete list of children with birth dates. The information in these documents can vary, but I have seen several that exceed fifteen pages and up. Pension papers are one of the few documents in your research that you will get a first hand account done by your ancestors. All of these records area available again at the National Archives.
My ancestor George Davey applied for a pension after he left the service. When he enrolled he had actually given the wrong year of birth. He was older than most when he signed up so his date he gave the government varied by ten years his actual birth date. Needless to say when it came time to apply for his pension he had a lot of explaining to do. His pension record had a great deal of documentation as a result.
Be sure to get your ancestors service and pension records from the Civil War. They offer extensive clues to earlier generations.