How To create new login (user) in POSTGRESQL in pgAdmin

Once connecter to the server. In left pane 

Right click on User/Login Roles -> select create -> click on user/login role

It will Open window to create Group role. In General tab you can provide the name of the user and Definition  tab you provide the password, expiration date (user will be automatically deactivated after the specified date and time) and connection limit (concurrently how many connection can be done through the user). In Privileges tab you can define this user can login (if it is unchecked it will be considered as role) to the pgadmin and have any super user permission such as create database, create role and inherit rights from parent option (be caesious this will give all databases access which are already assigned to the creating user). In membership tab you can add this user to any group