An email will be sent to all selected customers, guiding them through the account creation process when needed.
If you don't want customers to have to log in, you can also leave the selection in public access, and email separately the direct link to the selection on your website. You can edit the selection access rights at any time via the selection authorization panel.
If the images are not in any gallery, or if you want the customer to be able to make his own sub-selections, it is preferable to create a client gallery instead of a selection.