to get an answer to these types of questions, user experience designers, called UX designers, will do user testing, often in the form of A/B testing
while user experience design is also concerned with the appearance of the site, it’s how users interact with the site, navigating through and making decisions on where to click (and where not to click) that most strongly occupies a UX designer
typically user experience designers create wireframes, or visual blueprints for a site's design, as well as digging into information architecture, which is the fundamental way the information on the site is organized, displayed, and identified to users
fundamentally, user experience designers ensures that a website is easy to use, and provides products, whether information, a service, or items for sale, smoothly and efficiency
note that the field is relatively new, and interdisciplinary in nature, so degrees in psychology (most notably cognitive science), computer science, or graphic design could all be considered relevant