sale, sail

Sale or sale is the noun ( thing or idea ) form of  "sell"--
The sale of his childhood home brought tears to his eyes.
The school has asked for contributions to its bake sale.
The car dealer was pleased that he made the sale.
Sale often means a "special sale" or a temporary reduction in price--
Let's go shopping. They're having a sale.
The sale ends tomorrow.

Sail or sail ( rhymes with sale ) means to use a boat powered by canvas sheets. Sail may refer to the sheets of canvas themselves, or to the action of  gliding over the water, powered by the wind in the canvas sheets, or "sails"--
He wanted to learn to sail a boat.
The sailor used his spare time to mend the torn sail.
We'll need some wind before we can sail.
Sail is often used to mean any act of gliding through something in a way that seems effortless--
He was sure to sail right through the final exam, after all that studying.
He still remembered the way she would sail through a room.

Now that you know that, you can say--
"They bought a new sail when the boating  store had a sale."

Note--a "sailer" means a boat powered by sails--
This boat is a good sailer.
A "sailor" is a person who goes about on boats, including someone in the navy or the merchant marine--
He wanted to become a sailor, so that he could travel to distant places.
A "sailor" is a "sailor" even if the boat doesn't have "sails"--
The sailor worked all day on the ship's engines.