implement application for multiple users, starting with db

Hello, I wrote an texteditor with PHP,JS,mySQL that can extract data from JSON, write JSON files, display the update time etc.. I use 2 tabels in the db for 'sections' and 'items' (fields: headline / text) (1:n)

Now I want to implement this for multiple users.
I can write a log-in system using another table for the users, but then I stuff all the user data into these 2 tables.

I this is a common way to do this or are there better alternatives?
Thanks

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