To play normal mode, just follow the setup instructions on the quest card.
When you play normal mode (or easy mode of course) and if you're new to the game, you can also play the "Basic Game" defined in the core set rules:
Newer players or players who want a more basic experience can play and enjoy the game by not dealing shadow cards during the combat phase. This eliminates an element of surprise that could make the game too challenging for a beginner. Once players are comfortable with this experience, they can then add the shadow effects to make combat less predictable and more exciting.