Like a dancer circling a partner face-on, the Moon spins once per lap of Earth.
Earth's gravity pulls hardest on the Moon's near side, raising a rocky bulge toward Earth. The young Moon spun faster than it circled. Rock reshapes slowly, so the spin carried that bulge ahead of the Earth-facing spot.
Earth tugged the bulge back, against the spin, slowing it until one spin matched one lap and the bulge stayed put.