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As another answer mentioned, ROS is not a specific programming language. ROS let you easily develop your program without worrying how camera(s) and sensors work.

If you want to write programs using functions provided by ROS, you can take a quick view of these tutorials(especially 5~7. Node, Topic, Service are important concepts.)

Once you got some basic knowledge, you can try this tutorial to write a useful program by yourself, at that time you can fully understand what ROS stands for and how to write your program.