Just as design elements are important to the visual aspect of a web site, so is its ease of use. Most users visit web sites to get information or make a transaction (retail purchases, banking). Within a corporate intranet, web-based tools and applications help employees do their job. The key principle to remember is that usability is a continuous process. It's not uncommon for a web site to go through multiple iterations in its lifetime because just like anything else, there is always room for improvement.
Usability is a complex aspect because it not only encompasses the entire web site from front to back, but also factors in the user's thought process and actions. Web teams need to be aware that everyone thinks and interprets things differently. Will every visitor of your web site navigate it the same way? Have the same understanding? The answer is no. However, by following some basic steps you can increase the probability of user actions.
Site/ information architecture, labeling, interoperability, performance measures, and process architecture are just a few critical parts that may affect a user's experience and the site's overall success.
The bottom line: it shouldn't take a brain surgeon to navigate, find information or perform a task within your web site You can have the flashiest or most robust web site on the internet, but if folks can't find their way around, they'll go elsewhere.