Cristhian,
Welcome to the wonderful world of Mendix!
If you add the User Management snippet to a page that is used in the navigation for your app, you can add users at runtime with any user role(s). You'll need to create other user roles if you want more than the standard ones.
The Basic license is for a single app only.
Hope that helps you get started!
Mike
Thank you very much for your answer. Is what you mention about users also valid for the free plan?