Describe the qualities you have which makes you feel you are the ideal person for the position you are applying for?

Look at the job description. Pick out key Words that describe you. If you have time beforehand, make a list of the qualities they are looking for that also describe you.

They just want to know if you are a good match for the job. If you truly can't come up with any qualities that suit what they are looking for, you're probably applying for the wrong job.