1) put a copy of the job description in front of you
2) make sure you understand what is required for the position
3) put a copy of your resume in front of yourself and try to link the most part making sense. DO NOT MAKE UP ANY THING
in general, you must have something unique, find that is needed for the job functions, and fill it in
as for why you need this job, i would not put too much into that. if any thing you want expand your career and this seems to be the right career move for you
