Most Omeka sites consist of a searchable “collections catalog” of items. The next highest use of Omeka is the curation and publication of “narrative exhibits.” Once you have built an Omeka archive with enough items, you can then use exhibits to curate and interpret those items.
You can build exhibits of items and link them together with narrative or descriptive text for sharing. You can select a small number of items from your repository (potentially from different collections) and organise them into an exhibit. Visitors to your exhibit can click on an item and access its full record. Exhibits are made up of items that are grouped into pages (often with linking or explanatory text). Pages are then grouped into sections.
The exhibit builder plugin is included in your Omeka installation.
There is an accompanying Exhibit Builder guide on the Omeka site.