Angles can be obvious, and form the structure of a picture as here. Sometimes angle are implied by parts of the photograph. In this one the angles emphasize the vanishing point off the picture, drawing the eye up and making the viewer want to see more. Angles can also be used to remove the single focal point and add interest by creating a conflict of perspectives. Angles and lines can also give a subtle structure to a picture, allowing you to place the subject off centre and draw the viewer back to it.