Hi I just wanted to know what scope of content mean, in terms of writing an essay.

It means the 'subject matter'

From my experience I have found that a surprising number of students don't know how to construct an essay.

Basically, the introduction to an essay should outline the scope of your essay. In other words, the issues you are going to address in the essay. The content refers to the way you treat the issues outlined in your introduction in the main part of the essay.

Think of it like a speech.
A good speech has 3 parts: first you say what you are going to say (outline, introduction, scope), then you say it (taking as many words as needed, the longest part of the speech), then you summarize it (and include any topics/theories for future discussion).
You basically say the same thing 3 times albeit in different ways.