This story is not easy to summarize.
Look, I don't want to give out any further details about the plot other than this: it's the South Park kids-Cartman, Kyle, Stan, Kenny, and Butters who travel to Equestria. And everything else happens in Equestria. It doesn't get taken into the outside world. I just don't want to give out any more spoilers without you reading it. But I will tell you that this story is thrilling, hilarious, fun-reading, meaningful, controversial at points, unconventional for MLP:FIM fanfics, and motivational.
Also, I cannot emphasize this enough: read the author's notes at the beginning of the first chapter, please. Without it, you would be completely lost and all like "WTF" the entire story, stop reading early, and miss the entire point of it. It's that important, like you probably would want to take a screenshot or smartphone pic of it. If you're for whatever reason a non-brony, you should only really need to read the first part.