I'm not sure what information you are trying to search for. If you are interested in finding lists of soldiers who served in various regiments during the Civil War, you can go to the soldiers' and sailors' website, which is:
www.itd.nps.gov/cwssThis is an index to the compiled military service records at NARA, which were made from muster rolls, pay rolls, etc... You can search by soldier's name, or search for a particular regiment and get a list of the soldiers who served in that regiment. For more detailed information, you would need to order the service record and/or the pension file itself.