If you’ve more than one or two photos for a post or page, you can easily create a very basic gallery of thumbnails for the images, using WordPress’s built-in gallery system.

NOTE: You won’t have a Gallery tab until you’ve “associated” images with a particular post or page. There are two ways to create that association: 1) Upload an image while you’re on that post or page 2) Insert an image into a post or page from the media library. If you upload an image directly into the media library, it has no association with any particular post or page.