If the circus is coming to town and you paint a sign saying “Circus Coming to the Fairground Sunday”, that’s called advertising.
If you put the sign on the back of an elephant and walk it into town, that’s called promotion.
If the elephant walks through the mayor’s flower bed, that’s called publicity.
And if you get the mayor to laugh about it, that’s called public relations.
If the town’s citizens go the circus, you show them the many entertainment booths, explain how much fun they’ll have spending money at the booths, answer their questions and ultimately, they spend a lot at the circus, that’s called sales.
And, if you planned the whole thing, that’s Marketing!