Hey Aloami,
Here is where Mendix will shine for you in tremendous ways. I say it like this cause it’s arguably my favorite functionality.
First you would have to make sure your Domain model in place, then follow below steps (image for reference).
I think the easiest way to do this, is to create a page which is only visible for you and then show the corresponding data in a list view.
If you’re using the Administration module there even is a template for the user management inside the module.
If your question is how to query the database as a developer by directly connection to it. You need do it from Studio Pro, when you run the app, you can go to the Advanced Menu as below on the console and click on “Start Built in Database Viewer”.
A new window will open up, as below where you can run all your queries in SQL