How do nails attach to the nail bed?

When you get an injury on any finger or toe and it has that big red spot where the blood has collected it is necessary to relieve the pressure and put a small hole into the nail as the nail grows most of the time it will become detached from the nail bed you need to trim the detached part away and maybe cover with a band aid until it can grow out completely so it won't get caught on anything and tear into the corner that is attached and eventually it will all be attached.