In simplest terms, the major difference between a post and a page is that one is static and one is dynamic.
Pages are generally made up of fixed, or static, content on websites. You might update information on a page from time to time, but pages are usually predictable on websites. You can watch how to make a page here.
Posts, on the other hand, are usually made up of dynamic, or changing, content on websites. You can organize and arrange them according to tags or categories. You can watch how to make a post here.