For the general instruction manual, see docs/README.md.
The archives/, images/, multimedia/, and others/ subdirectories contain small, standalone files that can be used to seed afl-fuzz when testing parsers for a variety of common data formats.
There is probably not much to be said about these files, except that they were optimized for size and stripped of any non-essential fluff. Some directories contain several examples that exercise various features of the underlying format. For example, there is a PNG file with and without a color profile.
Additional test cases are always welcome.
In addition to well-chosen starting files, many fuzzing jobs benefit from a small and concise dictionary. See ../dictionaries/README.md for more.