To add people to your Business Manager-
1.Go to Business Settings.
2. Click People.
3. Click + Add.
4. Enter the work email addresses of the people you want to add and select the role you'd like to assign them. Then click Add People.
To add ad accounts. Go to Business Settings. Click Accounts and click Ad Accounts. Click + Add. Choose one of the 3 options: 1. Add Ad Account, 2.Request Access to an Ad Account or 3. Create a new ad account.