You’ve taken on the calling and you’re in the DM’s Chair.
What are you ?
You’re the umpire of the game. You interpret the rules; you don’t make up the rules. A large part of your role will be judgement calls, deciding the outcome of an event or occurrence or situation when the dice can’t. Apply logic and common sense. Make the call that is right, not the call that is popular.
You’re the god of your D&D realm. You’ve created the world and its geography, its demographics and flora & fauna and NPC’s and adventures waiting to happen. Yours is the power to create, invent, direct, and incite. Like a good deity, know the boundaries of your realm, its physics and its logic and its rules. Use your omnipotent power sparingly; set the realm in motion and let the players and the dice move the course of events. Allow for the implausible, respect cause-and-effect, and intervene as seldom you can.
You are the voice between your imagination and the players’ experience in your adventure. Narrate, describe, illustrate, enlighten. Build intrigue and curiosity. Present decisions and dilemmas for the players. Involve their characters in the realm they inhabit. Engage and interact with the players, get their ideas, work with them. Guide the story along, reacting to the players and their characters.