Themes change the public appearance of your exhibit: layout, colors and so on.
Click Appearance on the top menu. Choose one of the available themes by clicking Use This Theme, then view your site to see the changes.
You can change themes any time, so try out different ones.
Plugins add additional features to your site like social bookmarking, additional languages, or embedding PDFs. Click the Plugins menu at the top to see a list of available plugins.
For example: Click Install next to the Simple Pages plugin. This adds a useful new feature to the left menu: Simple Pages allows you to attach new pages to the site, for example to create an About page describing the exhibit.
This guide assumes you're creating an exhibit on Omeka.net.
You can install Omeka on your own server (consult your IT department and the Omeka help pages).
Exhibits created on Omeka.net can be moved to your custom Omeka installation using the API Import plugin.