The primary activity that you're likely to be doing on your WordPress site is publishing content. The content could be text you write, pictures you take, videos or audios (which may be hosted on another site), or other media that you've found elsewhere on the Web. WordPress makes it very easy to publish media content of all types, whether hosted on your actual Web server or elsewhere.
Out of the box, WordPress provides two primary content types for you two work with: posts and pages. If you read blogs or have ever written for a blog before, the concept of a post is probably a bit familiar. Posts often are content that appear on your blog in some kind of scheduled way. They usually are presented on your site in reverse-chronological order. Posts might be what you use to share your regular thoughts, reflections, or ideas about a topic. Posts make up a kind of "river" of content that you're producing as part of your blogging activity.
Pages usually correspond to our more traditional concept of what makes up a Web site. Pages are presented outside of the "river" of content that are posts. They are more likely to stand alone and be organized according to a traditional hierarchy. Pages might be content that is less frequently updated or changed.
If you were using WordPress to build a business Web site with a lot of information content, you would probably use Pages. If you added a feature to that site where you started to advertise special events or news, you would probably use Posts.
A few other things to know about Pages vs Posts:
Upon occasion, you may want to include media (images, audio, video) in your site's posts and pages. There are generally two approaches to handling media in WordPress:
Our general advice is to use externally hosted media whenever it makes sense and works. This is *usually* the case when you need to use audio or video; without plugins, well-presented audio and video in WordPress is tricky. For images, if you need to do basic editing and/or require different sizes of images, upload them to your site. Otherwise, consider referencing them from another location (your Flickr account, for example).
Recent versions of WordPress have built out a new "post format" feature which, if you are using a theme with the feature enabled, will style post formats differently depending on what they are. The formats that are built-in to WordPress (and are available for theme developers to use) are the following:
Those of you familiar with Tumblr may recognize this general approach.
For the most part, post formats are designed as a way to style a site (and customize styling depending on the kind of content that is being displayed). They have no special functionality, and their use depends entirely upon the theme you are using. Many older themes, for example, do not recognize post formats.
This is really a more advanced topic and feature of WordPress. Starting a few versions back, WordPress made it easier to create what are called custom post types. Basically, these allow you to define your own types of content for your special purposes. You can even define sets of custom fields for different custom post types -- allowing you to collect very specifically defined information. With this feature, it's possible to begin to turn WordPress into a more robust content management system or a system for data collection and presentation.