A hero's journey is a story template that you have probably seen a lot. It's how a hero is born and goes through the adventure of their life.
If you have kids or you are a kid at heart you would have watched a lot of Disney movies. I'm talking about the yearly blockbuster stuff, sorry Mickey you are getting a bit long in the tooth mate.
Even if you watch other adventure movies I'm sure you have or will notice this from now on.