The primary purpose of a user interface (UI) in software is to facilitate interaction between users and the application. A well-designed UI enhances user experience (UX) by making software intuitive and accessible. It encompasses elements like buttons, menus, and icons, which help users navigate functions and achieve their goals efficiently. A strong UI considers usability principles, focusing on clarity, consistency, and responsiveness. Ultimately, the effectiveness of a user interface significantly impacts user satisfaction and productivity in software applications.