A cover letter goes with a job applicant's resume and is sent to an employer to provide additional information about one's skills, experience and qualifications. Typically, if a cover letter is required, this is stated in the job listing.
An effective cover letter should explain why the applicant is interested in the position and that particular company. It should include contact information, a salutation, the body of the letter and an appropriate closing. If the contact person's name is given in the job posting, his name should be included in the salutation. It is not recommended to include salary requirements in a cover letter unless specifically requested to do so.