I just installed a new plugin, but it doesn't work at all.

The best way to install most plugins is using the Extension Manager. That way you will have the least problems. If you installed a plugin manually (i.e. extracted it into your wiki's plugin folder) or are using an older version of DokuWiki, the following might help.

• Make sure DokuWiki's cache gets purged by touching your conf/local.php. (Saving the configuration settings form over the admin interface works as well.)
• Make sure to bypass your browser's cache and force a reload of the relevant page (with Shift-F5, Ctrl-F5, Ctrl-Shift-R or similar).
• As a last resort, you may wish to delete the contents of the <dokuwiki>/data/cache/ on your server. This has worked in the past.

• A few plugins have dependencies (either other plugins need to be installed or some external applications). Check the instructions on the plugin's page if you have installed all required modules.
• Not all plugins work with all DokuWiki versions. Check on the plugin's page if it mentions any compatability information.

• Some download files (zip, tgz, etc) contain an incorrect file structure (sometimes due to automated zipping on hosted repositories like github.com). Check that there is a folder with the exact plugin's name, e.g. the plugin “gallery” should be in the folder named “gallery” (under ./lib/plugins/gallery). If the folder name is different, you should rename it to its correct name.