UX design process usually follows the prototype in an informal or formal usability testing process. This process happens before and even after launching of the website. This UX design helps to rectify some complexities in some kind of websites like multiple user, merger or acquisition and all.
UI design process most likely to interface human and designs. Which concentrate mainly on the front-end development, like tasks, workflows, more obviously simplifies whatever appears complex. As a result, it plays a role of bridge to connect programming and designing.