Hi Adil,
If you’re using the sandbox environment (free deployment) then you need to configure the users via Project Security → Demo Users tab. You can also try to add the users via Administration module as mentioned below but you need to configure atleast one demo role so that you can login as administrator and configure more users.
If you’re using a licensed cloud then you can use the Administration module → Account overview page to create more users for your application.
Hope this helps!