How does a hydrofoil float on water

An airfoil manipulates the flow of air to create and direct movement.
A hydrofoil does the same thing only in the water.
Although the term hydrofoil applies to boat rudders and keels as well as to the flippers, fins, and tails of fish and aquatic mammals, it's most commonly used to describe a ski-like platform attached by a strut to the hull of a boat.
When the boat speeds up, this hydrofoil pushes against the water, lifting the boat above the surface much the same way a wing creates lift.
While in ordinary circumstances increasing speed would increase drag on the boat, here, drag is minimized because most f the boat surface is moving against air rather then water, which is much denser.