I would advise a introduction course to UX design before something more technical, like mastering Sketch or Axure.
The Interaction Design Foundation is a great place to learn (online), check this: https://www.interaction-design.org/courses/become-a-ux-designer-from-scratch
Subscribe to Nielsen Norman Group newsletters, read the great articles they share every week or so.
If you want visual inspiration, there is Dribble and Behance!
I hope it helped.