A distraction is something that takes your attention away from what you're supposed to be doing. If you just can't keep from checking your email every ten seconds, that's a distraction that's going to interfere with doing your homework.
A distraction can also be a pleasant break. If you're worried about your dance recital tomorrow, watching a mindless action flick may be a welcome distraction that helps you relax. Has anyone ever told you, "You're driving me to distraction"? When you're driven to distraction, you're so agitated you feel like you're going crazy. Distraction comes from the Latin dis-, "apart," and trahere, "drag." So distraction is when you're dragged away from your task or from your worries.