Usable Web sites...
Usable Web sites help users achieve their goal easily, quickly, and pleasantly.
...and unusable Web sites
Many Web sites are not very usable. Some common reasons for this are a lack of clarity about the site's purpose or navigation, the use of unnecessary elements such as large graphics which slow page loading, and a failure to properly consider readability.
Usability testing
Web sites need to be tested by other people (not the site designer) to find out whether or not they are usable. One way to structure this is with "use cases" - imagainary users with imaginary goals, assigned to real testers to see what problems they have achieving the goals.
