How do high schools work in japan?

Question:

Like, I know that each semester you get some kind of summer break after. And why are there only 3 years? Can ya'll explain to me how they work, lots of details please

Answer:

Strange question. You don't get a summer break in the US? And there's three years of high school as compulsory education ends at 15, so HS is from 15 to 18.
A simple internet search would tell you this.