An application letter is a document that is attached along with your resume or C

An application letter is a document that is attached along with your resume or CV while applying for a job in a desired company for a desired position. An application letter elaborates on your academic qualifications along with the skills that you possess which make you an ideal candidate for the job role you’re applying for.
You can briefly emphasize your key skills and the experiences you have had in your past employment that make you an eligible applicant for that specific position in a specific company.
Adding an application letter is not a compulsion but is a recommended document that you can attach with your resume to leave a greater impact on the employer, allowing them to understand you, your skills, and your experiences more deeply as mentioned in the application letter.