Backward means "toward the rear" or "behind." It’s the opposite of forward. If you stop peddling your bike on a hill, you’ll start rolling backward. If you count backward from 10 to 1, you probably just hypnotized someone.
When you go backward, you move in reverse. You might give a backward glance at a person as you walk away. Backward also means "slow," or "behind the times," as in a backward government that doesn't allow girls to go to school. If you wear your clothes backward, then you’re dressing like Kris Kross, the hip-hop duo from the 90s. The Old English roots are on bæc, "back," and -weard, "toward." Backwards (with an “s”) is primarily British usage.