system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do the tips of our fingers and toes need a covering such as our nails?
gpt
Nails provide a firm backing, allowing for better grip, finer sensory function, and giving a handy pair of built-in pliers for delicate work.

Imagine you stuck a chopstick through a sausage, stopping a centimeter or so from the end.  Now try to pick up something small.  That stupid squishy sausage rolls around and you lose your grip.  Now add a spoon to the back of the sausage, lightly connected to the chopstick.  Now all that stupid sausage doesn't roll around as much, so you can pick things up.  In a pinch (pun intended), you can also use the edges of two sausage-spoons to pick up something very small.

That's the "what" of fingernails.  As for "why," well, they have a function which arose from modifications to the claws we inherited.  Why on the toes?  Because they're on the fingers.