VoiceOver is very well self-documented. You can press Control+Option+Command+F8 to start a tutorial, Control+Option+H to access the help menu and press it again to open the commands menu, which lists all the commands along with their shortcut keys. Finally you can press Control+Option+K to start keyboard help, where you can press key combinations to hear descriptions of what they do.

EDIT: Obviously this is after enabling VoiceOver, which you can do by pressing Command+F5 by default. On the Touch Bar MacBook Pros you will need to triple-press TouchID while holding Command.

Might not always be the best, but it's worth checking out AppleVis.com
For example here's a post titled "A Complete List of VoiceOver Keyboard Shortcuts Available on macOS"
https://www.applevis.com/guides/macos-voiceover/complete-list-voiceover-keyboard-shortcuts-available-macos

https://help.apple.com/voiceover/info/guide/10.12/

When you first turn voiceover on with a desktop/laptop, it brings you through a guided tour where you learn and can practice the various key commands and gestures for navigating the computer and the web. Turning it on in iOS, there is a practice area where you can play around with the different gestures to quickly understand how to navigate your device located directly in the VoiceOver accessibility settings.