From the introduction:
In order to play Teen Witch, you need a secret place. It needs to be a place where no one can see you, and no one can hear you as long as you only whisper. It needs to be somewhere where you can light candles, mark the floor, and whisper secrets.
Your bedroom will likely work, unless you share your room and the person is home. The forest will work. A bathroom or storage locker or attic might work, too.