Hearty describes abundant, full, and satisfying things, and lively, strong, and enthusiastic people. A bowl of thick chili with cheese and a glass of milk is hearty. A spoon of water with a grape? Not so hearty.
You can't miss the "heart" in hearty. Words like "wholehearted" and "half-hearted" also have "heart" and are a help in remembering the adjective hearty. If you put your whole heart into anything from walking a dog to saying good morning to your friends, you're hearty and full of life. Something half-hearted is weak and not hearty. A loud laugh that fills a room is very hearty; you can almost feel its fullness. If it comes from the heart and adds well-being and happiness, it's probably hearty.