OK, so, your database actually only needs one user (possibly also known as a schema, depending on your database), unless you want to limit who can do what.
Then, you need to configure your database to allow remote connections.
Once that’s done, you’ll be able to get something called a “connection string”, which can be used in your application to open a connection to the database.
Once the connection is open, you can use SQL to read/write/edit the database.
If multiple users are going to be doing this simultaneously, you will need to look into things like row locking, transactions, and isolation modes.
I hope that helps your research get started
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solved How to create a database that can be used by many users? [closed]