The left-side of the Solr Admin screen is a menu under the Solr logo that provides the navigation through the screens of the UI. The first set of links are for system-level information and configuration, and provide access to Logging, Core Admin and Java Properties, among other things.
After this information is a list of Solr cores configured for your Alfresco Content Services instance. Clicking on a core name shows a secondary menu of information and configuration options for that core specifically. Items in this list include the Schema, Config, Plugins, and an ability to perform queries on indexed data.
The different screens of the Solr Admin UI are described below.