You can create multiple websites in one registered account.
It is very easy to achieve that:
1.) Log into your account first and click on the website address bar on top that is displayed.
2.) Click now on "Create a new website" ("+").
3.) Enter the desired name of your new website (subdomain) and confirm by clicking on "Create website".
Now you have successfully created a new website into your account and can edit it as you are used to it.
For example, choosing a design template, uploading files, creating a page, etc.
But it is important that you always make sure that you are in the interface of the website that you really want to edit (especially if you want to delete that website).
To change your website, you don't have to logout and login again; it is sufficient when you click on the website address bar on the top, so that the selection of created websites is shown to you.
4.) Just click on the desired website, you want to edit, and you will immediately switch to the interface of that website and can make changes as you are used to.