To toss something is to chuck it. You might kill some time in your yard before dinner, where you and your sister can chuck a football back and forth.
When you chuck a tennis ball to your dog, you throw it casually and loosely. You could chuck pieces of bread in the direction of some ducks on a pond, or chuck a Frisbee around with friends after class. You can also chuck something away, or throw it away: "My old diaries? Oh, I decided to chuck those out." If a butcher talks about a chuck or a chuck roast, he means a shoulder cut of meat.