For a deep dive into those topics, you may want to embark on the side quest: design.
The difference of the two topics is easy to understand. User Experience (UX) refers to the journey of the user when using your product or website, e.g. the buttons he or she clicks, the processes she or he has to go through, etc. It’s about making a product more enjoyable to use. User Interface (UI) refers to the graphics and looks of your product, e.g. the colours, the shapes, the location of certain objects, etc.
For a first quick intro, you can watch to our friend Jesse Showalter, who provides a good overview: