Usability (UX) is about how easy it is for people to use a product or service. It focuses on how well users can accomplish tasks using the interface and their perception of ease and enjoyment during their interaction.
User Interface (UI) refers to a product’s or service’s essential visual design elements, like buttons or text boxes. It’s what you see when you’re interacting with something, and it’s what helps you to interact with it in the first place.