Hello @Akash,
if you mean adding table structure - not just data - then such change is not possible to do through web application directly, logical model including table and column definitions is managed in ONE Desktop application.
Adding users procedure varies - they can be added in Keycloak console directly under Users section, or in case you are connected to Active Directory or some identity provider they just need to be synchronized from the source. In both cases you need to ensure they have assigned relevant roles (again that might be manual assignment in Keycloak, or it can be imported from AD or identity provider). If you have admin permissions in RDM application, you should see permissions directly in the RDM application (button should be on left bottom part of the screen)
Kind regards
Tomáš