As you get more comfortable building agent, you will start to tackle larger problems, which are so large that it often may be better to break the task down to levels of difficulty, not unlike a game. After the problem is decomposed, it can be tackled with Curriculum Learning. Curriculum Learning is where an agent learns a task in stages or levels that increase in difficulty. It really is not unlike the way we learn a task as humans, for example, walking; we first learn to roll, then crawl, stand, stagger, and then walk. We have intuitively learned how to walk this way, but our agent friends need a bit of help, at least for now.
Let's go back to Unity and look at an example that is mostly configured for Curriculum Learning, ...
