This is a question. So I restored the topic type of Question instead of Discussion.

Have you read the https://forum.processing.org/topic/how-to-install-a-contributed-library sticky post?
When you are given /Processing/libraries/simpleML/library/simpleML.jar, the /Processing is actually the folder of your sketchbook, where you store your sketches, not where you installed Processing. And if the path gives 'libraries', you don't put a 'lib' instead.

Mmm, actually, if I read the first page you link to, it is explained quite profusely: " Processing now allows for a “libraries” folder inside your Processing sketchbook , which is a great deal more convenient than having your 3rd party libraries installed in the Processing application folder ." and so on...