Hi,
If you want ALL computers to be selectable by your users in the portal, you do not need to specify any criteria at all. Just leave step 2 "Configure Criteria" empty, and under step 3 "Display Columns", select the columns you want to be displayed in the portal.
If your users still don't see any computers, they are most likely restricted to see the configuration items based on the user role they are in. Make sure your user role for end users is not restricted by CI groups.
Regards,
Dieter