Photos can be viewed either individually (selected from the Files section), or in a sequence. That sequence can be from the timeline (chronological order), using the top arrows. You can also swipe left/right on the photo to go through the photos in chronological order.
Additionally, if in the Files screen you select a view mode which displays a subset of the files (e.g. bookmarked photos), you’ll get access to the bottom arrows, allowing you to navigate only through this subset. For example, you can use the bottom arrows to quickly find a bookmarked photo, then continue viewing the photos in the timeline, using the top arrows.
When you tap on the photo, you’ll also get access to a set of actions at the top to bookmark, upload, share, get details and delete that photo. Additionally, there is also an option (3 vertical dots) to set the orientation of the screen.
By default the orientation is set to auto, so the screen will switch between portrait and landscape, as you turn your device. You can also permanently set the orientation to portrait or landscape for all photos. If there is space below the photo, a map is shown marking the spot where you captured that particular photo (if GPS coordinates could be obtained at that time). But, if you keep your device in landscape orientation while viewing a landscape photo, then there will be no space for a map. If that is the case, turn your device to portrait to reveal the map.