There are lots of ways people act when they're scared. For example, you might watch a scary movie that scares you into sleeping with a night light. Or you might be too scared to try diving off the high board into a swimming pool. Now, if I see a big raccoon rummaging through our garbage, I might try to scare it away by banging a pot with a wooden spoon. Or if I'm hiking in the woods and unexpectedly come across a bear, just seeing the bear might be enough to scare me away. That mean, I'm running for my life!

To scare someone means to make him afraid. "The movie scared me." To scare someone AWAY means to scare him so much that he leaves. "I yelled at the dog and scared him away." In relationships (friendship, dating, etc.) we might say that you scare people away if do something that makes them stop hanging out with you. "Is John coming with us to the party?" "No, I think I scared him away by being so drunk last time."