What test does startup UEFI/BIOS perform when you first turn on a computer to verify it can communicate with essential hardware devices?

Power-On Self-Test (POST)

Explanation:

When a computer is turned on, the UEFI/BIOS will perform a Power-On Self-Test sequence to ensure that all the basic hardware connected to it e. g RAM, Keyboard, hard disks, are working properly. Faults are flagged, usually with a beep but this can vary between different systems and configurations