User Experience / User Interface
UX Design refers to the term User Experience Design, while UI Design stands for User Interface Design. Both elements are crucial to a product and work closely together. But despite their professional relationship, the roles themselves are quite different, referring to very different parts of the process and the design discipline. Where UX Design is a more analytical and technical field, UI Design is closer to what we refer to as graphic design, though the responsibilities are somewhat more complex. " Reference
The ability to understand the user journey, their experience using what you create and navigating them to where you want them to go is a complex art, From colours choices to layout, the design of a good user interface leads to a great user experience. Ux and UI are very important and go hand in hand.
FORM & FUNCTION
Unlike UX designers who are concerned with the overall feel of the product, user interface designers are particular about how the product is laid out.