You can have one website connected to one Zyro subscription. In other words, a single subscription allows you to host a single website.
If you need to host multiple websites, you will need to purchase as many subscriptions as many websites you want to have. Having one account, you can purchase as many subscriptions as you need, and they can be of different durations, too.
You can keep track of all of your subscriptions on the Subscriptions page in your dashboard.