Only "Owner" users can manage users.
You can view the list of currently existing users by clicking the "List" button next to the "Users" section on the "Configuration" page. Here is an example:
The above image shows the list of users have roles in the current auction. The user John Smith has the role selection opened to show the possible roles:
Clicking the delete option show a confirmation box. Deleted users will need to be re-invited.
Clicking the "Invite User" button (upper-right corner in above image) allows you to invite a new user. Here is an example invite ready to be sent:
The above image is inviting Mary with a role of "Normal" to the auction. Clicking the "Send Invite" button, sends an email to the user that looks similar to the following:
Clicking the "Register" button in the email invite will allow the person to create a BIDS account with the selected role for the auction.