What Does Illustrate Mean
This means being clear about what you are saying.
Think of an example of what an artist has drawn. In an article, you don't like pictures, you like words. So make a picture full of words and examples.
Ilrate = illuminate: distinguish or cultivate: clear the mind: make an example: explain.
So your teacher doesn't just ask for an explanation, he wants your explanation to be highlighted. You want an in-depth analysis of the facts.
Does it help?
Ever since he started compiling dictionaries, the definition of a word has become an illusion of its meaning. A very good dictionary will tell you where the word came from and, if necessary, how it is used. The last explanation.