UI vs UX
UI is what the interface is made of. UX is what happens to the person using it. Confusing them produces beautiful products nobody can finish a task in.
Beginner6 min readVanshikaDEFINITIONDesign
UX
User Experience
What it's actually like to use a product: whether the person knew what to do, how long it took, and how they felt at the end.
EXAMPLE
A checkout that asks for a delivery address before the user has chosen a delivery method is a UX problem, however well designed each screen is.
WHY IT MATTERS
Good UI with bad UX is the expensive failure, because it looks finished and passes review. Only watching someone try reveals it.