When you do something cheerfully, you do it in a happy or good-natured way. If you love walking your dog, you'll cheerfully grab her leash and head out first thing in the morning.
The adverb cheerfully is perfect for anything you do while whistling or smiling. If you do your chores with good humor, you do them cheerfully. And if you're excited and happy about making your grandparents their favorite dessert, you'll cheerfully spend the day baking a perfect apple pie. Cheerfully comes from cheer, which is defined as "optimism or joy," but originally meant "face," specifically the way the face expresses emotion.