Elaboration means "adding details." Kids are famous for answering "good" when asked how school was and "nothing" when asked what they did there. If pressed for elaboration, they might talk about recess, lunch, and even what they learned.
Elaboration is the result of going that extra mile, such as when your history teacher asks for five paragraphs on the Fall of Rome, and you write three pages, or when your friend, instead of giving you a regular birthday card, creates a mini-scrapbook with photos and mementos from the past year. As you can see, elaboration takes time and energy because you go into greater detail than usual.