Addons

• Directly in the backend: Add the line $se_upload_addons = true; to data/config.php. You can then install and update the addons from this catalog under Addons with a single click. For security reasons, this is disabled by default.
• Manually: Download the addon, unzip it and copy the folder via FTP to /plugins/ (plugins) or /public/assets/themes/ (themes).

An installed plugin only becomes active once you activate it under Addons or include it in a page.

• Plugins live in their own folder under /plugins/ and describe themselves in an info.json. Hooks let them tie into the frontend and backend without changing the core. With an update_url, your users see updates right in their backend.
• Themes are built on Smarty templates and can use any CSS framework. A theme only needs the templates it actually changes – everything else comes from the default theme.

Everything else is in the documentation: plugins, hooks and themes.