It's how your users navigate/flow through your site.

a design principle which advocates that a user's experience in interacting with a computer should involve a smooth and graceful dialog. In terms of the user's task, this means that response time should be rapid and user errors and error recovery should be rare. The "flow" refers to the movement through a user's task, and needs to proceed from one step to another without confusion and with minimal need for difficult planning of the following steps.

When "graceful flow" refers to the text in the interface, it suggests that readers should be able to read from one item to another without boredom and without pausing to try to make sense of the text or of an unusual transition.

Your website has to provide information that fulfills the immediate needs of your site visitors.

This is the fundamental principle behind usable website design, so let's repeat it one more time: Your website has to provide information that fulfills the immediate needs of your site visitors.

The immediate needs of the site visitors' are probably to answer questions like:

• Can I trust them?
• Are they any good at what they do?
• Will they get the job done?

To create the proper flow you will need to:

• Identify your users
• Know what you want your users to achieve whilst on your site
• Identify the information you'll need to provide to retain your users

The most important thing in usability is testing

If you don't do any usability testing you may discover that the structure of the website doesn't make sense once the website's up and running. This can and has happened and it leaves you with two choices: redesign the website or make a new website - neither are attractive options.