Your website’s usability is a necessary condition for whether or not you’ll get found and make conversions. If your website is difficult to use, then the search engines will rank you lower and your potential customers will leave. Plus, this is the most crucial factor in making a sale because customers will never buy from you if you make the buying process frustrating.
The word "usable" means that something works well in its simplest form. It means that a person with the most limited ability or experience can use something - a website, a mobile phone, an espresso maker - for its intended purpose without getting massively frustrated. A user's experience on your website should be thought-free. You shouldn't assume that they read your finely crafted text or weigh their options before clicking through on any of your links. Your customers are on the hunt for something specific, and at best, they will glance at a page or two.
Website usability offers a better return on investment than almost any other business action online. It’s comprised of how search engines view the backbone of your website and whether or not customers will stay once they get there. Visitors of a usable website can find what they want quicker and do what they want easier as well.