What is a pronoun...
A pronoun can replace a noun or another pronoun. You use pronouns like "he," "which," "none," and "you" to make your sentences less cumbersome and less repetitive.
In this case 'it' which I feel sure was actually decipherable in that the first two referred to the same thing, the IDE compiler, not much else was involved to give error messages! The third followed Arduinoscope which is an object and so that is what it referred to.
I know you really are a teacher in disguise 
The presumptions that 'you' make are that I am naturally English speaking and that I am not a person with learning difficulties.
However, I stand corrected!!! I apologise for my hurried and poor grammar and hope that you are not offended by my response. I also know that I should not have put exclamation marks in the body of this sentence.
Here goes...
The Processing IDE issued a error message when I attempted to compile 'simpleserialarduinoscope.pde'. The message indicated that The package "Arduinoscope" did not exist and that I might be missing a library. I was then told by the Processing IDE where to place the library when and if I found the library.
The reason that I was running Arduinoscope in the IDE and not running the executable provided was because I had made changes to parameters within the source file.
I suspect (presume) that all the files and folders provided in the downloads that I mentioned in an earlier post in response to an earlier admonition, are not required and that in itself has caused some of my confusion.
I have been unable to find a comment (which I must have missed) in the book
that I have read twice, that explains where the files go. I suspect that the folder network provided is not in a usable form exactly as the folder nest is provided. Some items appear to require moving and I am asking for somebody to kindly help me work out precisely which items go where in the system that I have got set up which is...
A Arduino Folder above Sketchbook above libraries and a Processing folder above Sketchbook above libraries.
When I know the answer that I seek, I feel sure that it will serve me well in future endeavours of this nature.
It is also very easy for those to whom this particular aspect is second nature, to forget that their is a first nature.
You need to start Processing, load a sketch, then run that sketch.
I did and received the error message to which I referred a few moments ago. Though I think I know, you didn't say which Sketch.