Database split up in company names

I am working on an app where companies can register their coworkers. At signup i want them to type the company name.
I need the company name to be registered in the database so that the user is owner/administrator of that company. Afterwards all the user that this owner register will automatically be in that company.

The scope of this is that different companies should be able to register in my app and have their own restricted access to the company table in the database. The only person that is able to signup is the the owner. All other user will be registered by the owner. This is instead of creating a sub-app/domain every time a company signup.

Does anyone have an overall idea to do this in the workflow and in the database structure?

Or will it be best if I use sub-apps for each company?