Since UX stands for “user experience”, the main focus of UX design is the end user's experience of the product. A user's experience is determined by whether their interaction seems logical, smooth and easy, or whether it feels confusing, random and a struggle. In a nutshell, user experience is determined by how easy or how difficult it is to interact with the user interface components.
UX designers do a variety of things, depending on the project and its state of development. Working in UX typically involves elements of research, testing, business analysis, project management, wire framing, and psychology.
In earlier stages of a project (the foundational stage of UX design), UX designers will do preliminary market and user research (for eg. focus groups, online surveys, interviews etc.) and then plan out interactions by wire framing and prototyping their projects. UX is determined by understanding a user's needs and goals, so user research helps to get into the mind of the target audience. UX designers will then test through various heuristics as well as with actual external users in order to develop fictional representations of real end users. During development they continue analyzing, testing, and iterating at various stages of development, working with both UI designers and developers to improve on the product and its interactions. After launching a product, a UX designer may analyze user metrics to track the outcomes of their work and go back and continue to iterate on any points of friction they may have noticed.