The Domain wizard is the last step. The wizard will ask for the details of your branded subdomain. 

The branded subdomain will represent a link that includes your agency name and the niche that you are targeting. It would be a good practice to have a unique link to have your landing pages hosted and white label this link using your domain. 

Related Articles:

Agency Integration Settings
Agency Settings: Branding
Agency Settings: White Label
Agency Settings: User Setup
Agency Settings: My Templates
Agency Settings: Notifications