I am reposting a couple of links to websites that provide detailed descriptions of the microfilmed records of the Freedmen's Bureau that are available at the National Archives. The descriptions form what are called "descriptive pamphlets," hardcopies of which can also be ordered from the Archives.

***** Site #1 (National Archives' own webpage, same as hyperlink at bottom of this posting):
http://www.archives.gov/research/african-americans/freedmens-bureau/#view

***** Site #2 (from the St. Louis County, MO library's website; has same info as at website 1 above, but also includes other guides to National Archives records beyond those involving the Freedmen's Bureau):
http://www.slcl.org/branches/hq/sc/dps/dplist.htm

These same links could be found by doing a thorough search of the Reconstruction Period Research forum, but the titles of the posts in which they lie might be confusing for a newbie (such as myself).

Note: According to a statement on one of the National Archives' webpages, "Copies of field office records microfilms are available for viewing at the National Archives Building in Washington, DC, and at each of the regional archives" [i.e., Alaska, California, Georgia, Illinois, Massachusetts, Missouri, New York, Pennsylvania, Texas, and Washington state]. However, I don't see the records listed in the catalog at my nearest regional archives (New York City), so I am not sure whether this statement is accurate. The microfilms are certainly available for review or purchase at the Washington DC location.

To find the guides at website #1, scroll about halfway down the page and look to the right; for example, under "Field Office Records on Microfilm," you will find a link to a PDF file of the the descriptive pamphlet for Louisiana's microfilmed records (microfilm series M1905).
I noticed that at least one of the hyperlinks is dead (the one to Alabama). To get around this, you can take the series number that is displayed (in the case of Alabama it would be m1900) and substitute that number into the following link in place of the xxxxx (be sure to use a lower-case 'm' at the start of the series number or you will get a "file not found" error):
www.archives.gov/research/microfilm/xxxxx.pdf

So for Alabama, it would be www.archives.gov/research/microfilm/m1900.pdf