[Theme: Graphene] Adding a photo gallery to my site

I’m working on a site using the free theme Graphene but I didn’t realize it didn’t come with a photo gallery option. I really like the theme otherwise, but I need 2 different pages with photo galleries on each page. Unless someone can suggest a similar looking theme that comes with a photo gallery option built in. Should I use a plugin? How do you use that? I’m sorry, I’m very very unfamiliar with WordPress and just trying to figure out how it works.