Use of comma with "and"

The latter one is correct.

Man, I always hated these when I was in school. For me, it was based on the preference of the teacher, but both were considered correct. I always wrote mine like the first one, though.

The word and replaces the comma. 'Apples, oranges and grapes' is correct and looks better. However, either IS correct.

First one is grammatical hundred percent correct but usually we use second one.

The important question here is the use of the word "and." If the items in the list are not units, the comma makes more sense before the "and."

I bought apples, bananas, pears, and grapes.
You do not want it to sound as if the pears automatically appear with the grapes, as it were.

However, if the last two items are a unit, you do not want to separate them.

I saw the Beatles, The Rolling Stones, and Sonny and Cher.

You do not want to separate Sonny and Cher because the "and" is part of the term. Ham and eggs, salt and pepper, Laurel and Hardy are other examples.