This manual page is not meant to be exhaustive. The complete documentation for this version of TEX can be found in the info file or manual Web2C: A TeX implementation.
The patgen program reads the dictionary_file and produces the pattern_file, writing a transcript of its actions on the log_file. The dictionary_file should contain a list of hyphenated words and previously-generated patterns.
The patterns thus generated can be read by initex for use in hyphenating words. For a (very) long example of patgen's output, see $TEXMFMAIN/generic/hyphen/hyphen.tex, which contains the patterns TEX uses for English. At some sites, patterns for several other languages may be available, and the local tex programs may have them preloaded; consult your Local Guide or your system administrator for details.