The main domain you use is considered as one license.
Once you decide to connect a subdomain, or use a totally new domain, this will be considered as another, one license.
Here is how it works:
domain.com can be your main domain. If you create multiple, unlimited tabs, for example: domain.com/bloginstall - this will still be considered as part of your one domain, although the pages can be completely different.
However, if you decide to create a subdomain, for example: blog.domain.com - this will be considered as a separate domain by the system (and once you set this up, it will be considered as an extra license).
Depending on your iGloo Plan, you will generally either have 1 or 20 domains you can connect your pages to. If you have reached a limit on the amount of domains you have used inside your iGloo account and would like more, please send us a screenshot and your purchase receipt in a new ticket.