To calculate a total for only one user, you will need to create a relation column that links the user email to all the orders that contain that email. Then you can create a rollup column against that relation to get a total only for that user.
Here’s some information on User Profiles. Once you enable them, them you will have access to the user profile information for your visibility condition.
https://docs.glideapps.com/all/reference/privacy-and-per-user-data/user-profiles