Using the custom shape tool
How to add extra elements and shapes to your image is to use the Custom Shape Tool. It is easy to find on the Tool panel which contains tons of geometric shapes by default.
There is an extended options available to further work with the custom shape tool.
How to find it? It has an icon containing a puzzle.
Tip on bringing up more shapes – click on the small arrow at the panels right side once again for a whole list of shapes to appear. This contains way more options than the usual geometric shapes.