What is UX/UI, and how does it affect your sales?

A site that "looks nice" is not the same as one that is "easy to use". That difference decides whether a visitor keeps going or leaves.

The difference in brief

UI is the look — colours, buttons, type. UX is the feeling while using the site — did you find what you needed easily, or did you get lost?

UI is the look. UX is the feeling of using it. Both matter, but they are not the same thing.