Written job applications usually include a cover letter and resume.
A cover letter is a statement addressing the key selection criteria.
A resume is a document that briefly summarises your knowledge, skills and experiences.
A cover letter is a short (about one page) letter where you can introduce yourself to a potential employer. It usually contains:
some brief information about you
what job you are applying for and the reasons why you’re interested in the job
some of the skills that you can offer the employer
your interest and availability for an interview.
You can check out Youth Central’s How to Write a Cover Letter page for detailed advice on writing a cover letter. On the bottom of the page, there are additional links for specific situations, like how to write a cover letter if you don’t yet have work experience.