Sail is a piece of fabric attached to a ship and positioned such that it causes the wind to move the boat along briskly on water.
"The sail of is an important piece of the ship.
Sale is an exchange of good and services for cash or fund in an auction to the highest bidder.
"I've put the car up for sale."
Sell means an agreement to transfer goods or provide services in exchange for money. This is usually preceded by haggling on a specific price between the buyer and seller.
"Janet plans to sell the house if she could not get the loan eventually to raise money for her sister's hospital bill."