How to automate the creation of databases on a website, based on user login?

Supposing a site that has a member system, in which the user logs in and registers, such as Facebook, how do I get the user to create his account, a database is automatically created for him? The only way I was able to do it on my system is for the user to register and I manually create a database for it, but this seems to me a lot of work as the number of users grows, and the user will have to wait to receive my system