Could someone please explain the three act structure and hero's journey structure and how they work, please?
Act One in a nutshell: Put your character in a compromising position. Chase them up a tree. "Incite conflict." These are all saying the same thing.
Act Two in a nutshell: Your character comes up with a solution to the problem and fails. Your character comes up with another solution and fails. Repeat until they come up with a solution that works. Long stories have more, short stories have fewer.
Alternatively: Character comes up with a solution and succeeds, but creates/finds a new problem. Rinse and repeat.
Act Three in a nutshell: The fallout of the solution. What changes? How do they change?
The heroes journey can be roughly equated to a change in mentality before and after "the story." Generally a character whose mentality remains the same before and after is an adventurer (character of an "adventure") as opposed to a hero (character of a "story").
This very, very approximate explanation of literary theory brought to you by CIW.