If enabled in a search result template, theicon will appear in the search results. When clicked, a preview of your record will open in a pop-up window.
To enable Record Preview, tick the 'Enable Preview' option in the search result template.
The fields shown in the preview pop-up are controlled by two settings in field maintenance: the 'Public' and the 'Opac Summary' tick boxes. The former controls whether an end-user is able to see the field while the latter controls whether the field appears in the preview, for all record types. This can be further modified at a more granular level using record type template maintenance.
For example, you might want a field to be shown for your Book record preview, but not your Journal preview. You would tick the 'Public' and 'Opac Summary' boxes in field maintenance and then disable the 'Opac Summary' box for the Journal record type in record type template maintenance.