I really need some help with Gallery

Hello, all - I may be having a really dense day but cannot get to grips with this. I have everything on my new site working except for gallery. Its installed and I can click on one of the test pages such as gallery/example-d/ So look, we just have one gallery. I want to be able to load this in style D with a main image and thumbnails below. I suppose I should have a path like gallery/album.php?s=test but just cannot figure out if that should go on a template - if so where - and what should be on my actual gallery page? I would really appreciate any help on this - feelling rather foolish and promised client it would be ready this week. Thanks much.