To create new user in SQL Server Management Studio 17, Open SSMS and connect to the SQL Server as a System Administrator. This can be done by logging on locally using Windows Authentication, or externally by using the ‘sa’ credentials.
In Object Explorer, Right click on “Security” in the left pane, and select “New”, then “Logins”.
In newly opened window, enter the desired user name in “Login Name” field and select “SQL Authentication“, then enter the desired user password. Ensure to uncheck the “Enforce password expiration” option.
Select your database as the Default database, and click on User Mapping on the left side. Click the check box next to your database, and then check “db_owner” checkbox in “Database Role Membership for”.
Lastly, click OK to create the login and database user.