For this period there are two main series available in microfilm, depending on the publisher, "Records of the Department of State Relating to ..." and "Confidential U.S. State Department Central Files." The microfilm series are arranged by country and date. A little of this material is now available online in Archives Unbound.
Records created from 1910-1963 were arranged according to the decimal filing scheme: http://www.archives.gov/research/foreign-policy/state-dept/rg-59-central-file.html#decimal. See also Purport lists for the Department of State Decimal File, 1910-1944 [microform] -- this is an index to the documents in the decimal file. The complete set is 654 reels; CRL holds many.
Records created from 1963-1973 were arranged according to a subject-numeric filing system. http://www.archives.gov/research/foreign-policy/state-dept/rg-59-central-file.html#subject briefly describes the arrangement of these records.
Publication of material from 1963-1966 has only begun recently. Some is available on microfilm and some is available online.
Records created from 1973 through 1975 were entered into an electronic State Archiving System and may be available in the National Archives Access to Archival Databases system: http://aad.archives.gov/aad/
