Photoshop software is written in C++ and many such graphics application can be developed by using programming languages and C/C++ being the very famous language for such jobs.
Whatever application you are using needs at least one programming language (tool) to develop it and if you are good at such programming, you can either manipulate or use efficiently those programs or you can even build of your own based on your requirement.Can you imagine about photoshop or any such tools without programming language? Even this website is developed using programming and your O.S. is also written using programming languages only :)
Think programming languages as thread (building block) and photoshop as cloth made by using threads :)If you need further explanation, then please let us know. Ask any question in details so that we would be able to understand the question more and will be able to answer with more details :D \m/