You can choose from many types of node: blog posts, stand-alone pages, interlinked book-like pages, and many more.
Your node options
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You'll see a list of all the node types you can create (which may vary by site). Here are the chief ones for a typical web site:
Blog Entry node
What it is: A piece of blog, or "web log", content. If you're uncertain what that is, don't worry; we all were, just a short while back. While there's no strict definition of blog, it typically refers to a series of online stories, musings, or other "posts".
What to use it for: The Blog Entry is most useful for any diary- or record-like content, consisting of (usually) short pieces listed by date. Good uses for the node type are company news items, short daily reports, and your random thoughts or frothing rants.
What it is: A generic page, with no specific assumptions on how you might use it.
What to use it for: Pretty much anything that doesn't better fall into another, more niche node type. Product pages, a company overview, any sort of general information – these are all standard uses. Many organizations' sites use a Page for general information about the organization and what it does.
Book Page node
What it is: Book Pages are like Pages, but are designed for easy organization into groups and sub-groups, like the sections and chapters of a book. You set a "hierarchy" of pages, with a "top section", pages grouped into "chapters" beneath that, a chapter's pages grouped into "sub-chapters", and so on, as many levels deep as you like. Drupal creates appropriate navigation links automatically.
What to use it for: If you want to create an online "book" from web pages organized into a certain structure, this is the way to do it. One excellent application is a user manual – like EDAM. These instruction pages are built using Book Pages, letting me easily organize or re-organize them by topic, sub-topic, and so on.
What it is: The original creators of Drupal had envisioned some differences between the Page and Story formats, but the two have apparently merged into pretty much the same thing. You can think of a Story as simply another version of a Page.
What to use it for: What good is having two versions of a generic page, one called Page and one called Story? There doesn't seem any reason to set out building the system that way, but as long as Drupal has developed with those two forms of pages, you can put them to use if you like.
Since you can configure how each content type behaves, you might use Pages (to conjure an example) for general information content that only administrators create, and use Stories for content that any registered site user can write and submit. Or use Pages for company background info, and Stories for product info, if you have reason to keep their content types separate. Or set up Pages to display no author name and posting date, and use them for general information; set up Stories to display author and date, and use them for news articles. It's up to you.
If you don't see an immediate need for the Story format, ignore it. Later, when and if you find good reason to deploy a second type of general page, the Story node type will be waiting.