For all users, to view your current storage on your Amber X, log in to the Amber X OS web GUI and open the File Explorer application.
Click on the Settings [gear] icon in the top-right corner.
You can see your usage next to Home Folder Quota. You can set a quota for users as the admin following this tutorial here.
Admin view: You can also view the dashboard as admin in Control Panel.
Click on the Volume submenu to give you more info. Note this is total storage used by all users.