How can I create new users in Workspace 365?
Creating new users can only be done by an Administrator from within the organization. As Administrator, you can go to User Management via Settings. With the "New" button you can create a new user. When creating a new user, you will be given the option to also create this user in Office 365. Importing existing Office 365 users can also be done: click "Import" and make your selection (from Office 365 directly or using a CSV file).
If your Workspace is created using an ordering system (e.g. Parallels/Odin), User Management is organized within the ordering system itself.