Primary means written at or near the time of the historical event.
Secondary means written many years later, probably by a scholar researching the historical event.
War of the Rebellion: a Compilation of the Official Records of the Union and Confederate Armies (HTMLfrom e-History). You can also search Cornell University's image copies of the War of the Rebellion. Reports, letters, telegrams, and general orders from the War Department. This is a primary source.
Civil War Maps from the Library of Congress. This is a primary source.
Civil War Soldiers and Sailors System National Parks Service search of individual soldiers. This is a primary source.
If you would like to order information about your ancestor who served in the Civil War, follow the instructions on this link.
Nationwide Graveside Locator Burial locations of veterans and their family members in VA National Cemeteries, state veterans cemeteries, various other military and Department of Interior cemeteries, and for veterans buried in private cemeteries when the grave is marked with a government grave marker.
Southern Homefront Documents from UNC Charlotte's Documenting the American South history website. Southern Homefront includes Southern life during the Civil War. Collection includes over four hundred Civil War era maps, broadsides, photographs, printed works, Confederate currency, and manuscript letters and diaries. This is a primary source.
You can find some primary sources in books. Below is a list of relevant subject headings. When searching for these in the catalog, try adding "sources", "documents", "correspondence" or "letters" to your search.