User research is used to understand the user’s needs, behaviours, experience and motivations through various qualitative and quantitative methods to inform the process of solving the complexities that users face.
User Experience Design is the method of designing a system to best suite the users needs. This includes making information readily available to users. Understanding the users thought process and placing buttons and data where the user is most likely to look for it. The result of optimizing user experience design presents an opportunity to engage in a dialog that guides users' information needs.
Designers aim to create designs users will find easy to use. UI design typically refers to graphical user interfaces but also includes others, such as voice-controlled ones.
Usability testing is a way to see how easy it is to use something by testing it with real users. Users are typically asked to complete a task while being monitored by a reasercher to observe where they encounter problems and feel confused.