You’ll need to look at firstly setting your Administrator account username and password.
https://docs.mendix.com/refguide/administrator
To setup named users you’ll want to look at using the Administration module in the App Store folder. Add it to your navigation and you can then use the Administrator account you setup earlier to create new users and assign roles to them.
Hope this helps.
Implement the administration moduel fro the app store for example.
See: https://appstore.home.mendix.com/link/app/23513/Mendix/Administration-module
My suggestion would be to implement the Appstore app SystemManagement https://appstore.home.mendix.com/link/app/113984/.
Thank you everyone, that is the part I was missing.
Regards