After installing your plugin (see FAQ Article - Install your first plugin), most of the time you have to setup user-group permissions and plugin settings.
When you download a plugin from the CMS website there is always a readme.txt file in the package. Please read it carefully and follow the steps to setup the plugin successfully.
1. Install the plugin
2. In user-group change access for each user-group
3. Configure the plugins and add content.
1. Go to plugins/hooks and uninstall the gallery plugin