* Making the squares is trivial, once you went through the tutorials (or look at the examples). Hints: rect() and fill().
* Reacting on click on a rectangle is less easy: Processing has no notion of clickable object, once the rectangle is drawn, it is just a bunch of pixels. So you detect the click (eg. with mousePressed() callback) at the whole sketch level and check that it is within the bounds of one or the other rectangle.
You can also make your own Rectangle class to make smarter rectangles...
* Trivial.
* Send the info: you can use link(), although it might spawn a browser window. Alternatively, you can use Java stuff to invoke an URL, I used that to upload data (images).
It would look like:
Code:

	URL url = new URL(uploadURL); // throws MalformedURLException
	connection = (HttpURLConnection) url.openConnection();  // throws IOException
	connection.setRequestMethod("GET");  // With GET method
etc. 

and of course, the userChoice parameter put after the URL.