plugins directory is used for installing plugins which will be activated or deactivated from the private area’s plugin configuration administration page. Plugins are typically downloaded using FTP and extracted into this directory, one sub-directory per plugin. The existence of a directory called
plugins/auto that is write accessible will enable webmasters to automatically download plugins from within the private area interface without the need to use FTP or to UNZIP the plugins manually.
The most recent collection of plugins is located at http://files.spip.org/spip-zone/, but other plugins may be available from other sites. As with any externally contributed code, be very careful what you install, and if in doubt, only use plugins from SPIP’s own collection.