mmm....when I was in HS (long ago, but dipolomas were not carved in rocks!) you took the AP course (I took American History, english and biology) you took the course and were graded just as if it were any other HS course. But then in the spring you took the AP test. That test was scored on a scale of 1-5. I got 4's across the board, and earned a year of college credit for each test/course. Now, unless things have changed, you don't just get college credit by taking the course, you have to take the exam. Otherwise, it is just a HS course. But perhaps things have changed and they did away with the test, grading the work differently. As I said, my HS days are part of American History to be sure!
Now, my son who is a senior this year is taking an english/rhetoric class that is also for college credit. He is simultaneously enrolled at the junior college and got a first semester grade from the college, in addition to his grade on his HS report card. But it is NOT an AP course. It is structured differently. I don't think our rural HS even offers AP courses for test taking purposes. But they do this concurrent enrollment in certain classes. Meets the same purpose without the test - the HS kids earn college credit for higher level coursework.
I suppose the reason to take the AP courses would be to earn the credit while in HS so there's fewer required courses to take, less tuition money to spend and more freedom to take preferred or major-related courses while actually in college. That was the advantage for me. I started college with enough credits to almost be a sophomore! Saved tuition!
