Hi Sean

Box is one of the supported repositories with Totara - you will need the Client ID and secret from the box developer page to link the reporsitory.

Once connected then you would use the file picker in Totara and choose a file from the repository - you can choose to make a copy or link to the file in the repository. If you link to the file in repository than any chanes to the files in repository will be reflected in Totara.

Regards