Adding items and images to your website
Items
Items are the building blocks of the Omeka system.
It will be easier to add images to your site first, so that you can select them while building your pages. To add any image to your site, whether it's a gallery item or supporting decorative image, you have to create an "item", which is found in the left hand menu under the Resources section.
Items are listed in the Items tab (one box icon), found on the left-hand navigation of the administrative dashboard.
See full user documentation about items in Omeka here.
Item Sets
Think of creating an item set as making a category to organize your items. You can also think of it as a collection of artwork or artifacts. They make it simpler to locate items when you search by item set as your collection grows.
Item sets are managed via the Item Sets tab (stacked boxes) located in the left navigation of the admin dashboard.