There are a few ways to add Client Users.
Admin – manually add Client Users to Company > Users pages. You can import a CSV file of users or add them one at a time. Once added, you can invite them to complete the registration process and then login. (Note: only Senior Managers can mass invite users)
Senior Managers – can manually add their co-workers.
Self Registration – works in two ways.
If you allow Client Users to self register on the general Storefront page, Client Users will be asked to create a ‘Company’.
To have Client Users register for a particular Account, Admin needs to enable a private login page for that client and then activate ‘Allow Self Registration’.
Video: Adding Users