Member App doesn't have limits for the number of memberships you can create or the number of domains a user may connect to their account. By default a user is given one platform subdomain name at registration. This platform subdomain is ready to be used for publishing a membership on it and for accepting payments.
A user can not only connect a his own custom domain to Member App, but create any number of subdomains on his custom domain. Hosting companies don't charge for subdomain creation and such domain can equally be used for publishing a membership. See this article for useful tips on organising you membership websites.
To understand the difference, we must first have a look at how the domain name system works. Domain names are organised in levels. The first level of domain names is top level domains. For example:
Second level domain names (are usually called simply 'domains') is what people can purchase from domain registrars:
Third level domain names or simply subdomains (subdomains of a second level domain name) can be added fro your domain in the domain registrar's dashboard:
Adding a subdomain (singing.online-education.net) to Member App works in the same way as a domain (online-education.net) - by creating an A record in domain name servers. The important difference is that the A record must be created for the domain or its subdomain respectively.
Connecting a subdomain
To connect only singing.online-education.net to Member App, use 'singing' as Host in your DNS records. This record will only affect singing.online-education.net and not online-education.net. Your domain online-education.net may host a completely different website at the same time, for example, a landing page.
Connecting a domain
To connect only online-education.net to Member App, use '@' as Host in your DNS records. This symbol has a special meaning: records with this symbol will be applied to second level domain itself. Some domain registrars allow you to leave this field empty, which will produce the same result.
Connecting a domain and a its subdomain at the same time
You may connect both your subdomain singing.online-education.net and your domain online-education.net to Member App at the same time. They can be used to publish two different memberships. To do that, we will need to create both A records from the examples above. The correct records will look like this: