The first list contains all the available tools in TOra. If an item is selected in the list it is enabled. If unselected it is not enabled.
There is also a combobox at the bottom called Default tool. Using this setting you can specify which tool to start by default when opening a new connection. Many people are for instance more interested in the database browser than a worksheet and could start that instead of a worksheet by default on opening a connection.
Be aware that you need to restart TOra for changes to these settings take affect.