A writer's voice is a lot like obscenity; you know it when you "hear" it.
Voice isn't the story, it's all of the choices that the writer makes in order to tell it. Dr. Seuss has a distinctive voice. So do Jennifer Weiner, Stephen King and Bill Bryson. You could file off all of the most distinguishing markers and still know who is telling any given story. Jennifer Weiner could tell a spooky story set in Maine and you'd still know it was her telling it.
Voice also takes a hell of a long time to develop. It's easeir to imitate the voices of the writers you love when you're just finding your way into the craft than it is to find your own. And that's fine. It's all part of the process.
For today's exercise, I'm going to give you a story outline, then you need to develop it while focusing on *your* voice. The outline: College-age man meets college-age woman. They fall in love. Complications ensue, yet they all live happily ever after (if not necessarily together).