You can create a user account for a customer through the back-end. There may be cases where a customer can not register for some reason, and you'll want to create an account for them so that they can utilize your website, in an effort to prevent them from getting frustrated with the process.
You can do this by:
Logging into the CMS
Navigate to "Browse" and "Sites"
Click the site in question.
Click on the link that says "Users"
Click the link that reads "Add User"
Input the username, password an email address.
Click the button that reads "ADD".
This will create a regular user for this customer, as if they created it themselves. Although this customer will not have any membership attached to this account. You can add a membership if needed by clicking on Edit membership.