Expand the Security > Logins folder to show a list of users.

Right-click on the Logins folder and select New Login... from the contextual menu.

In the dialog that appears do the following:

1) Set the login name. This example uses odbc_user but you could also choose something like screensteps_user.

2) Set a password using SQL Server authentication.

3) Turn off Enforce password expiration

4) Set the default database to screensteps_workgroup.

Now switch to Server Roles (1). Make sure public and sysadmin are checked (2).

The new user account will appear in the Security > Logins folder.