Sailing boats have sails. Aerodynamically speaking, a sail is a wing.
But the angle of a sail relative to the air moving across it, the wind in other words, is controlled and adjusted by means of ropes and pulleys.
Tremendous force (and usually a winch) is needed to set a sail so that it cuts through the wind at the correct angle and creates the lift that moves the boat.
And then the problem becomes keeping the sail at the correct angle.
The boat may turn, which turns the sail with it.

Or the wind may shift, changing speed and direction all on its own.
In every case, the angle must be readjusted manually, that’s what is meant by trimming a sail.

No human sailor has reflexes fast enough to keep up with wind that shifts second by second.
The fastest racing sailboats in the world use wings, but they are still operated like sails, using ropes and pulleys and winches.
A self-trimming wing works totally differently, it’s controlled by its tail, like the wing on a plane.
The wing/tail unit acts like an airplane flies, except that while the elevators on a plane’s tail send it climbing up or gliding down, the angle of the tail makes the wing pull left or right.
It’s the same basic action, just rotated 90 degrees.

A hard wing on a free-rotating mount with a tail, is more difficult to design than a mast, which is a simple pole held up by guy wires, but the payoff is in the actual sailing.
By severing all the ropes that run between the boat and the sail on a normal yacht, a lot of the complexity of sailing goes away.
In a normal sailing boat, every turn of the rudder turns the sail.
Not so with a free-rotating wing, which by its very nature is always correctly angled into the wind.
Furthermore, dialing in the amount of sideways lift generated by the wing—thrust, in other words, is a matter of adjusting the angle of the tail.
Which is in effect a "throttle".