You can use your Ad360 Account to run advertising operations for yourself or on behalf of multiple customers, using one or several sub-account entities called "Agency".
It's up to you to decide how you want to organize your Account and Agencies. You can set up, for example, one Agency per Customer, or one Agency per division at your enterprise, or any other division that makes sense to your business.
Users that you will create can then be assigned to a specific Agency, in which case they won't be able to access the entities and data related to other Agencies.
Within each Agency, the following entities are used to structure advertising operations: Advertiser, Campaign, Line Item, Creative, Segment, Site List.