To send create a new login for a user, you need to login and have administrative rights. Go to Site Admin->Site Setup->Users. Beside each user you will find a series of icons, to create a login for a user click the Setup User Login button. This will automatically create a username and password and e-mail the information to the user. If you do not see the Setup User Login button, it means the user does not have a primary e-mail address set up. You will have to add an e-mail address by clicking the Edit User button.