As a noun:
* The buoy bobbed gently on the waves, marking the location of the shipwreck.
* The sailors used a buoy to mark their fishing spot.
* The lifeguard threw a buoy to the struggling swimmer.
As a verb:
* The news of her success buoyed her spirits.
* The strong economy helped buoy the stock market.
* His friends' support buoyed him during his difficult time.