MLA
Johnson, D. F. Letter from D. F. Johnson (Camp between [?] and Fredericksburg, Virginia) to "Dear Mrs. Sarah," Johnson Was a Member of the 3rd Battalion, Georgia Sharpshooters - August 17, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 12. https://digital.library.emory.edu/purl/433dz08mr9-cor.
APA, 6th edition
Johnson, D. F. (1863). Letter from D. F. Johnson (camp between [?] and Fredericksburg, Virginia) to "Dear Mrs. Sarah," Johnson was a member of the 3rd Battalion, Georgia Sharpshooters - August 17, 1863 (Box 4, Folder 12) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/433dz08mr9-cor.
Chicago
Johnson, D. F. “Letter from D. F. Johnson (Camp between [?] and Fredericksburg, Virginia) to ‘Dear Mrs. Sarah," Johnson Was a Member of the 3rd Battalion, Georgia Sharpshooters - August 17, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 4, Folder 12. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/433dz08mr9-cor.