Shapes in your photo give a geometrical structure within the photo that lets the brain more easily understand what it is looking at. This makes it more attractive because the person looking at the photo can make sense of the image. Triangles and curves work well in particular.
Here is an example of a curve. Always be prepared to take photos from low down or high up to show a different angle of view. This photo was taken from the floor to show the spiral of the staircase.
This photo also has a curve, and it has diagonals as well.
Triangles are also interesting to include in your photo. The three points of the triangle don’t always have to be linked by lines because the person looking at the photo will connect them together when they are looking at the image, like this:
Triangles can be created from lines in the scene, and the edge of the frame can use used as one side of the triangle. You can see several triangles in this photo formed by the jetty, the boats and the edge of the frame.