Earnings are the amount of money you make from doing a job. You'll be a lot more excited about babysitting when you learn your earnings will be more than generous.
Most earnings come from work that you've done, although money you earn from an investment can also be called earnings. Any financial profit or gain you make go into the earnings category, since you earn that money, whether through work, luck, or intelligence. The Proto-Germanic root, *aznon, means "do harvest work."