Step1: If you have not already created a gallery then first create one through
the "Media gallery Manager Module" and add a few media to this gallery.
Step2: Once a gallery is created, go to "admin options" page of this module and select the gallery you
want to display. You can just choose the gallery for the first time and press save.
Later visit admin options again to further refine how gallery will like.
Step3: (optional) if Comment moderation on media is on then use the comment
moderation page to approve/disapprove media.
(you can visit this help again by clicking on module actions->help)