A site is composed of several types of content, with each serving a specific purpose. Together, these types of content make up the site tree where you can add new content types and navigate the sections of your site for easy updating.
A page is the most commonly used content type. Think of it as a blank canvas for text and images, similar to a word-processor file.
Forms are a set of input fields to collect information from your site's visitors. For example, a contact form.
A gallery is a collection of multimedia elements. For example, a photo or video gallery. (See: creating a gallery.)
A link is used to manage a single link within your site, often one that is outside of your site's domain. For example, a link to your Facebook page or Twitter account.
A folder is a shell or container for other content. It can be used for structuring the content of your site, such as footer links or sidebar content. It can also hold the place of a link that contains no data, such as the top-level of a drop down menu.
A blog content type enables you to write chronologically listed posts . It also includes other common features you'd expect from a blog, such as comments, categories, and an RSS feed.