XPO comes with 2 types of account management capabilities: Partner Account Management (PAM) and User Account Management (UAM).
Use PAM if you want to manage multiple advertisers. PAM comes with a Partner Admin account which you can use to create and organize advertiser accounts or for different product divisions and so on.
Partner Admin has full access to the specific partner-level account and all advertiser-level accounts under it. Partner Admin also has the right to grant different levels of user access across the advertisers. More information about user roles and permissions can be found here.