Here are the main UI elements you should know about. This list is not exhaustive but you’ll find great ideas and inspiration for your next app project.
There are lots of UI kits available online for download. A UI kit is a set of files that contains critical UI components like fonts, layered design files, icons, and design components. There are several formats depending on the software you use for prototyping (Adobe XD, Sketch, Illustrator, Figma…).
Apple and Google provide UI resources for designing great apps that integrate seamlessly with their platforms:
iOS Human Interface Guidelines
UI Guidelines for Android