Hey there:
An important question first, are you playing using Orbiter 2010 or Orbiter 2016? I only ask because the DGIV has not yet been updated for Orbiter 2016, and if you're trying to use it in that version of the simulator, you won't be able to use it fully due to incompatibility.
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As for tutorials on how to operate the vessel? Tex Films' "The Orbital Elements" beginner tutorial video series is a great place to start with getting acquainted with orbital mechanics and general MFD usage.
Here is a link to those videos. For a quick jump into the DGIV's systems in a practical setting, his "Earth to Mars" video was very helpful to me when first learning the DGIV.
Here is a link to that video. He goes through a number of the ship's systems and general procedures in that video.
Additionally, David Courtney has provided some amazing video tutorials you may find useful to you as well. He is
@blixel on the forums. An absolute legend of an Orbinaut.
Here is a link to his YouTube channel.
I hope you find these resources useful to you.