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 displayed on top.
2.) Click now on "Create a new website" ("+").
3.) Enter the name of your new website (subdomain) and confirm by clicking on "Create website".
You have now successfully created a new website into your account and can edit it.
For example, choosing a design template, uploading files, creating a page, etc.
You may now choose a design template, upload files, create a page, etc. But it is important that you are always 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; just click the website you want to manage on top of the interface so that the selection of created websites are shown to you.
4.) Just click the desired website you want to edit and you will immediately be switched to the interface of that website you want to make changes with.