UI design is the visual look of an app or website.
A good user interface will help users find what they are looking for quickly and easily. Which helps you convert users into customers.
Through usability testing we can refine and optimize the UI over time.
UX design removes all friction from the interface between human and machine.
This doesn't only apply to apps and websites. UX design covers all products and services.
It's about streamlining a process, requires a lot of research and testing, user flows and wireframing out ideas.