The "Installation History" tab lists the history of provisioning operations performed on the system. Here previous configurations can be identified as previous states of the system. A state/configuration can be simply identified by the set of installed features. When you perform a provisioning operation such as installing/uninstalling of features, system state/configuration change occurs.
You can revert the current configuration to a previous configuration. In this process, some feature might get installed and some might get uninstalled. When you click on a previous configuration, you will be able to see this information.
Click "Revert" to revert the current configuration to a previous configuration or "Back" to return to the previous page without any changes.