In many job applications, you attach an application letter to your resume.
Actually, the letter comes before the resume.
The role of the application letter is to draw a clear connection between the
job you are seeking and your qualifications listed in the resume. To put it
another way, the letter matches the requirements of the job with your
qualifications, emphasizing how you are right for that job. The application
letter is not a lengthy summary of the resume — not at all. It selectively
mentions information in the resume, as appropriate.