The fundamental parts of UI/UX Design I'll recommend you should learn are as follows:
Complete beginner's guide to user research
The UX research process in product design
What is design thinking and why is it important?
How to apply design thinking to the UX process
What exactly is design thinking?
Button design: Types of UX buttons and best practices
7 basic rules of buttons design
UI design: Basic types of buttons in user interfaces
Designing states for buttons and UI interactions