1. Wait for pressing of any key.
2. When keypress occurs (correctly debounced), disable interpreting input from all keys, perform related action,
3. Wait for clearing of the keypad (release of this key and all other keys that might have been pressed in the meantime) - recognizing release performed using debounce
4. Re-enable reading and interpreting all keys, go to 1.

Raghu just means that if user presses 2 or more keys at the same time, bad things may occur. We read and process only the first and until the last (even if only one) is released, ignore all the rest.