With Workspace you are able to register multiple environments for multiple customers.

Binding an Office 365 tenant to a Workspace 365 environment is the first step when setting up the workspace.
Multiple Workspace 365 environments can be linked to one Office 365 tenant and a single Workspace 365 environment can be linked to one Office 365 tenant. You can not link multiple Office 365 tenants to one workspace 365 environment.

Each environment must be created with a global admin of the corresponding Office 365 tenant. Make sure this account has a mailbox enabled. During registration, workspace sends a confirmation e-mail to that account. This global admin account has to remain active in the workspace for workspace to function. For more info on how to register an environment, contact your Workspace 365 Administrator or Submit a request.

After you've received the e-mail, make sure you navigate to the URL listed in the email. Log in with the credentials that are provided to you in the e-mail.

After you have logged in, you will be prompted to set up Single Sign-On.