The devices pane is where you'll see the MIDI controllers you'll be using in your session. The first step after connecting your devices is to go to Tools > Options, and there in the MIDI section select the devices you want to use. You can then go in the MIDI Devices tab, and there you have the option of renaming them with a clearer alias. You can also flag some of them that shouldn't appear in the software./
This done, you can configure the default device that is added automatically there and/or add new ones with the "+" button.
Click on the devices for further info.