Every user has own database - how?

Hello

How create something like this:

UserName: user1 (he's root db_user1)
DatabaseName db_user1

UserName: user2  (he's root db_user2)
DatabaseName db_user2


I'd like create several users and several databases, ever user should
be root only for own database

Could anybody show my SQL example how do this, please. I'm new in
postgresql, I've used mysql

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Best regards