One important area for new WordPress site owners is the difference between pages and posts. Let’s try to clear that up.
Posts are entries usually listed in reverse chronological order on your site. There are some ordering exceptions, but the common element of posts is that they appear in some predefined order. Think of posts like posts in a journal or diary. They are not necessarily related but tell a story (sometimes) over time. Generally posts are categorized and tagged so that they may be found easily. It would be very unusual for individual posts to appear on your menus.
Posts are most often associated with a blog. Readers can subscribe to your blog and any new or changed pages will be pushed out to them. These subscription feeds make it really easy for others to keep up on your content without having to visit your site for any updates. Rather than coming to your site for updates, the updates are automatically pushed to them!
Pages are static (they stand by themselves and don’t change much) and are not listed by date. Pages do not use tags or categories. Pages are usually linked to your menu. When a reader clicks on a menu they are taken to a page. An About page is the classic example of a page.
Pages and posts cannot be interchanged. In other words you can’t transform a post into a page or vice versa. Of course, you can cut and past content between a page and a post to move content from one type to the other.