Hi Avinash,
In addition to the information already provided by my colleagues and to answer your question, you'll need to understand the two types of users that exists in OutSystems and how you can manage them.
In short:
IT Users are users like developers or administrators that need to access Service Studio, Service Center or Lifetime. These users can be managed in Lifetime --> User Management (not in Service Center)
End Users are application users that need to access OutSystems applications that exist in your environment. These users can be managed in the Users application.
Hope this helps.
Regards,
Nordin