To install a new module on SilverStripe, follow these steps:
Browse to the SilverStripe add-ons website and navigate to the module you wish to install.
Follow the instructions to install it with Composer. For example, to install the “starter-theme” module:
cd /opt/bitnami/silverstripe/ composer require cwp/starter-theme 3.*@dev
Browse to http://SERVER-IP/silverstripe/dev/build and click the “Run the action” button to rebuild the database.
Browse back to the application and the module should now be installed.
For more information, refer to the official documentation.