How does BIOS communicate errors?

Answer 1

The bios reports errors on the start-up screen. Simply white on black. It reports any failures to start up correctly, for example if an operating system is not found, or a vital component is not functioning.
If the screen memory or basic video cannot be accessed, the error can be signalled by a series of beeps from the onboard sounder. The exact meanings of the beeps, will have to be looked up in the motherboard instructions.

Answer 2

The errors would usually come up in POST (when you start up your computer) as a series of beeps and/or lights (depends on your computer's system board) if it's hardware-related (take the processor or RAM for example). Otherwise, it will be shown on the screen indicating the error.

Answer 3

Beep-code, flashing front panel light, on screen error message