This compositional element is so powerful that you will direct the viewer’s eye to the object and create more structure in the photo. This photo above is a combination of a Frame within a frame (the tunnel and arc of it), Leading lines (the railway) and a Symmetry (the railway and tunnel).
In photography, a frame within a frame is when the photographer uses something within the scene in front of them to frame the main subject.
By using a frame, you can create more visually interesting images, but you have to be purposeful in how you incorporate a frame into your images. Compose your photos with a strong frame, within a frame, and you will see a huge improvement.