According to its website, Processing is:
an open source programming language and environment for people who want to program images, animation, and interactions. It is used by students, artists, designers, researchers, and hobbyists for learning, prototyping, and production. It is created to teach fundamentals of computer programming within a visual context and to serve as a software sketchbook and professional production tool.The guys who made this language were really smart about it. It's based on Java, but they abstracted away the parts nobody wants to worry about, least of all the beginner. For instance, reading and writing files and drawing to the screen are made to be very easy no matter whether you are using your program on your own computer or as an applet on the web. This can be very tricky without Processing.
To see what awesome things can be done with Processing - and the code that goes with it - check out Open Processing. The best way to get started is by looking at other peoples' code and playing with it to see what changes. You can also read the tutorials on the official website, and check out Learning Processing.
My first little game made in Processing is called Bottle Sort. Share with us what you make!