It's called the Oxford comma. ;-)
how can we use "comma" if we wanna say some things that mean discribe them?
two delimiters in a list is crazy... please do not help make more crazy grammer rules... It adds absolutely no value.
If there is no comma, the last two items seem to be one. For example: I ate an apple, a slice of pizza and chips. This makes it seem as though the pizza and chips were eaten together or otherwise separated from the apple (and makes it seem the comma should be followed by another "and").
Yes if it is a list of individual things: apples, beans, and rice. No if two things are meant to go together: I ate some apples, beans and rice, and dessert.
If you say: 'I ate an apple, a slice of pizza and chips' it doesn't sound to me as though the pizza and chips go together. However if you say: 'I ate an apple and a slice of pizza and chips' then it would sound as though the pizza and chips went together. (lol it would also sound as though the chips were served on the pizza). But I may be wrong. Please correct me.