All modules are installed inside the subdirectory "mods" of your Phorum installation directory. There are two types of modules: single file and multi file modules.
Single file modules consist of a single
php-file containing also the description and
hook-names. These kind of modules can't have
a settings-page.
You install a single file module by simply
dropping its php-file into the mods
directory and enabling it in the
administration pages.
Multi file modules consist of at least a
directory with a php-file named the same as
the directory and an info.txt-file.
Additionally for a settings-page there needs
to be a settings.php. Beside these
standard-files there can be all kind of
files and directories used for the module's
functions.
You install a multi-file module by copying
the whole directory (preserving its
directory structure) into the mods-directory
and enabling it in the admin.