If you are an Admin within your organization, you will see an "Account Members" item under the Admin menu.  If you click that item, it will take you to a list of the current members in the organization.  

Click the Add New Member button.  

You can then fill in the new member's name and email address.  The new user will be sent an email notification to complete the process.   

Note that the initial password link expires after 5 days.  Should the member not log on to their account and change their password before the 5 days are up, they can request a new link using our "forgot password" function: