How child theme functions.php over rides parent theme functions.php

I am looking for a link to an article or help on understanding how child themes and parent themes functions.php work.

I know with CSS, the cascade overrides CSS declared earlier in the style sheet. It is my understanding that the functions.php does not operate the same way. I understand that both functions.php are loaded.

What happens if you want to have the function in the child theme override a function in the parent theme and the parent theme is not using if statements like the codex recommends?

Thanks in advance.