Where do you see yourself in five years?

By asking this question the interviewer is trying to establish how committed you are to staying within the company for a long time. The answer to this question will help in deciding whether they should continue with your candidacy or not, since the employers don't like a candidate who shows the symptoms of leaving them after they have invested in training them.
First thing you should do is to go through the job description and company's mission and vision statement properly. Then think how this job aligns with your future plans and might help you in achieving them.