UX is about understanding who your users are and what the problems they’re trying to solve are, then organising flows, content and layouts to help them achieve it.
I’d recommend reading Lean UX by Jeff Gothelf as it’s a good introduction to a flexible, user-centred approach to product design.
I’ve heard good things about the Google UX course on Coursera if you want to go into more detail. Interaction Design Foundation and Baymard Institute have a lot of great information.