Easy navigation is the foundation for good website usability. If your visitors can't get to the information they're looking for quickly, they're going to go to someone else's website to get the information. Sending visitors packing is anti-marketing.
So how do you create a website that's so easy to navigate that your visitors don't even have to think about it? You use global, local and contextual links. You supply a site map or a site index to guide users.
Global and local navigation are the ubiquitous menu bar items that get visitors from one section of the site to another in a quantum leap. The obvious purpose here is to, well, get visitors from one section to another quickly.
The first step to effective global navigation is to break your content into logical categories. Think about who your audience is. You likely have more than one type of reader and can group content geared towards these various readers. This will help determine the global navigation.
Within these broad categories you can break down the content into smaller bite-sized pieces using local navigation menus.
This needs to be done so it flows logically. In the example below, Intuit uses broad product categories and more specific product versions as the means of global and local navigation. Just what you'd expect to see.
Contextual links are the links from within the page text. This is a great way to provide more detailed information on what your talking about.
Let's look at AListApart.com. Where a term might be confusing, or benefit from further explanation, they use contextual links to send readers to other articles with more detailed information.
Site maps allow you to present an outline of all of the pages on your site so visitors can scan all of your content quickly. These are really helpful in a "I don't really know what I'm looking for but I'll know it when I see it" scenario. Just be sure to keep this up-to-date.
Regardless of what kind of navigation structure you're using, content needs to be organized in a way that makes sense to your visitor. Good site design and good navigational structure is all about website usability. And that's just good marketing.