Easy, but easy to forget if you're a mouser -> A Beginner’s Guide to Manual Accessibility Testing with Keyboard Navigation

https://www.sitepoint.com/accessibility-testing-with-keyboard-navigation/

A Beginner’s Guide to Manual Accessibility Testing with Keyboard Navigation

Learn the 5 essential keyboard commands — Tab, Shift+Tab, Enter, Spacebar, and Arrow Keys — that developers and designers need to manually test website accessibility for screen reader users.