What is the difference between user experience and user interface? and which part is important for a good mobile application?

User experience always comes first for workable interface.

Best example is to design any interface, start with "Sketch/wf. "Sketch/wf" part is experience, in which you decide the flow of work. After that you make it attractive by colors and shape, which is called Interface.

user experience is the outcomes a user generate from using/interacting with a user interface design of a system!

How i sees it, user experience will help you design a better user interface design for your mobile application.