There are a lot of compositional elements in photography. One of them is framing. I quite often use this element to get a certain perspective of things, to create interest and to put the main subject into a context. Frames can also be helpful to get a needed foreground or some shallow depth of field leading towards the subject. There are natural frames like rocks, trees or shadows and there are plenty of artificial frames like windows, hallways, fences and arches. In all of these cases frames lead the viewer's eyes straight to the place you want it to go.