Please explain the differences in user permissions/roles.

Below are the differences for each user permission for your reference.

Approver: Can view and operate all promotions.
Additionally, only approvers can set/change payment information such as credit card information.
Can add new users with permissions below the approver level.

Operations Manager: Can view and operate all promotions.
Can add new users with permissions below the operations manager level.

Operations Staff: Can only view and operate promotions linked as their responsibility.
Can also create new promotions as their own projects.

View-Only User: Can only view promotions linked as their responsibility,
and cannot perform any operations.