When you do something jubilantly, you do it with great joy and enthusiasm. If your best friend moves away but comes back to surprise you for your birthday, you'll probably react jubilantly, with laughter and hugs.
Anything that's done jubilantly is full of so much happiness that you want to shout with joy and excitement. In fact, the Latin root is iubilare, "to let out whoops" or "to shout for joy." Use this adverb for things worth celebrating, like when you jubilantly announce to your family that you've won a major prize, or when your soccer team jubilantly celebrates finally winning a match after a losing streak.