How UX and UI work together

UX concerns the experience of reaching a goal. User interface design shapes the controls and information through which people interact with a product. Interface decisions include visual hierarchy, labels, states and feedback, not decoration alone.

In a ticket app, choosing when seat selection happens affects the journey. Making available seats distinguishable and showing which seat is selected are interface decisions. Both influence whether someone can buy the right ticket.

These responsibilities overlap and teams divide them differently. The useful distinction is the question being answered: does the journey support the task, and does the interface make each action understandable?