The position of the adams apple changes your resonance - the length of the resonance chamber above your vocal chords. The goal is to make this resonance chamber smaller. Position of the Larynx (which may be detected with the "adams apple") plays a role, but also tightness of the muscles around the "tube".
What instructions are you following, it is a youtube video, a text description, something you talked about with people or given to you by a voice coach?