Websites and apps all need an interface. The interface is the first thing which faces the user. Better user experience depends upon how better is the user interface (UI) and a better user interface stop user to get frustrated.
There are two questions you should ask yourself to improve interface:
Is it useful? –
The functionality of an interface needs to work in order to complete the user desired task.
Is it usable? –
The task should be completed by the user in an easy and effective manner without any sense of frustration.