A web designer is free to focus on the entire project while a UI designer is constrained to one particular component of the program's development. The part of the program that a user interacts with is developed by a UI (User Interface) designer. A web designer is someone who works on the layout and creation of a website or page. If you are a beginner and want to start your career as a UI designer and to become web designer then I suggest you go for the Intellipaat UI UX design course which their courses are designed in such a way anyone can learn from ground level to advanced level.
For your reference, I am attaching Intellipaat’s complete free course video