Connection to the Arduino: above all else, DragonFrame needs to be connected to the Arduino so that it is possible to send orders. In the 'Scene' menu, click on the "Connections" submenu… to bring up the following window:

Make sure that the control module is connected to the computer, then click 'Connect' in one of the four ArcMoco zones (note that the first one of the list is not one of them). Be sure to check the "Connection required for shooting" checkbox to avoid launching a shooting while the Arduino is disconnected. Remember the selected area ArcMoco number, it will be necessary later.
At the connection, DragonFrame asks you to select the USB connection from a drop-down list: normally, one of the possible choises has the name of your Arduino model.

Once validated, the connections panel displays the status of the Arduino and the version of the sketch that has been loaded.

DragonFrame knows now that it is connected to an Arduino. If the connection should be broken, you would have to get back to this window to reactivate it.