Why do violins have "f" holes for sound on violins?

I could give you a technically sounding BS answer that nobody could understand but that would make me look like an "A" hole...LOFL

To let the sound out.

They have had F-shaped holes since the 1600s.  The F-shaped holes allow a more robust sound than the predecessors which included C-shaped holes,  round-shaped holes, and half-moon-shaped holes.