In the basic level, UI (User Interface) is pages and all the visual elements, like buttons pictures from the design side, that makes a person use the service or product. UX (User Experience) includes everything that you can see screens and it's structure, keyboards, sounds, colors. However, the UI is created based on personal taste and style of a designer, UX is made only based on researches and analysis of the users'preferences. Without UX there is no UI either you have a pretty product that doesn't meet the users' needs and complicated to use. But from the other hands, there is no UX without UI, or the result will be just a bunch of practical and technical screens that doesn't look like a usable product that the user expects.