Settings → Plugins. Everything installed in the system is listed here.
Installing
A plugin is a folder in custom/Plugins. Copy the folder onto the hosting and the plugin appears in the list by itself and creates its tables. Delete the folder and its record is removed.
If something went wrong during installation, the row is marked: the plugin is not fully installed. Check write permissions and database access, then press “Reinstall” in the row. Reinstalling deletes the plugin’s tables and settings and creates them again — whatever was configured is lost.
Active
A toggle in the list. A disabled plugin takes no part in the import and shows none of its tabs.
Order
A whole number from zero. It decides in what order plugins are applied to a product, and that matters more than it looks: if two plugins change the same field, the result depends on which ran first. For plugins that touch the price, set the order explicitly instead of leaving zeros.
Where the settings are
A plugin has its own settings page, opened from the list. It does not get its own item in the side menu — it adds a tab inside the section it belongs to: markup goes into “Prices”, an export into “Export”. That is why the menu does not grow with the number of enabled plugins.
Some plugins have no settings at all — the row says so.