Here's an outline of the items that should be included in every cover letter.
Header
A cover letter should begin with both you and the employer's contact information (name, address, phone number, email) followed by the date.
Salutation
Begin your cover letter with "Dear Mr./Ms. Last Name." If you are unsure if your contact is male or female, you can write out their full name. If you do not know the employer's last name, simply write, "Dear Hiring Manager."
First Paragraph
Begin your introduction by stating what job you are applying for. Explain where you heard about the job, particularly if you heard about it from a contact associated with the company. Briefly mention how your skills and experience match the company and/or position.