What is the difference between arrangement and combination?

A simple arrangement of no elements taken P The P, where n> = 1 and p is a natural number, is any ordering of P elements among the no elements, where each way of taking the elements is differentiated by the order and nature of the elements.

That is, in arrangements also matters to order of the elements while in combinations only matters to nature, ie the elements must be different.

For example, if we want to know how many doubles we can do with 5 volleyball players, we have to use combination, because in a duo what matters is the nature (the players must be different), that is, the duo João and José is the same. double that Joseph and John, so we should not tell it.