The conversion rate refers to the percentage of visitors who take a desired action such as subscribing, buying or joining. For example, the conversion rate of visitors that subscribe to a newsletter is the number of visitors divided by the number of subscribers. Clearly, you want your conversion rate to be as high as possible. The goal of usability testing is to help you to improve your site and raise that conversion rate. So if your conversion rate from visitors to buyers is 1 percent, making the changes we recommend could increase it to 2 percent… and double your revenues!
Whatever the main task of your site, you will need to know your conversion rate. Use Google Analytics to create a "goal" that you can analyze and determine if the changes you're making are improving your conversions.