1.) Create a new instrument track by dropping the instrument into the arrangement.
2.) (Optional) Enable separate output channels for each instrument using the instruments-tab in the mixer and in the EZDrummer-Mixer.
That way, you get separate mixer channels for mixing the individual drums, which is pretty handy.
3.) Assign a midi-input-device and channel.
You must create it in the "external instruments" section of the StudioOne preferences. Just choose the midi-input-port you are using to trigger the drums. In the video I choose my VMK-88-Controller-Keyboard.
4.) Record arm your track and enable monitoring
You should now be able to play EZDrummer using your hardware midi-controller.