There are pages, static content that you do not want to enter into discussion about, or posts. WordPress Posts offer you the ability to write content that is relevant to your site, product, or area of expertise and build a following. They can provide your site with a means to build back-links (further information on back-links to follow) which will add value and subsequently increase your position within Google.
If you are running a food website then you could be posting recipes, nutritional info, methods for preparing, where you source ingredients etc etc. This format applies to many different disciplines and enables you to use your website to generate interest for your users.