WMT - Adding New Users
Use the User Management menu item to see the list of current users. To add a new user, click either the "Add User" link in the sidebar or the "Create User" button on the right hand corner.

On the Create User screen, enter the Name, Email, and Password for the new user.
Clicking the little ABC123 icon in the right end of the Password field will generate a random password.
Make note of the password to share with the new user.
Click Create.

Once the new user is created, they now need to be assigned a role:

The Attach Role button brings up a modal window. Select the appropriate role and then Submit.

Follow these same steps if a role needs changed.