A resume contains all the direct details relating to the skills or experiences you possess to perform the duties of the job. Often, a resume can be widely distributed to different organizations with minimal changes to make it unique to the organization. On the contrary, a cover letter should be unique to the organization. It should provide details of the specific position you are applying for; you can include the job title or position number. If you were referred to the job by a current employee, be sure to mention his or her name. Please be sure the referring employee is in good standing with the company; otherwise, do not mention his or her name. 
Many job sites offer the option to include a cover letter. It is wise to include a prepared cover letter for your submission. If you are submitting a resume via e-mail to a recruiter, you can include a prepared cover letter as the body of the e-mail. A cover letter can include details which are not obvious from the resume or which provide the opportunity to elaborate on skills you were not able to include in the resume. Similar to your resume, a cover letter should be relevant and concise. It should also be grammatically correct and formatted as a letter with a proper salutation and signature.
If your resume contains all course work experience, your cover letter could elaborate on your interest in the position and describe how your course work experience relates to the requirements of the job. There is one thing to consider: recruiters may not always understand the requirements of a position and how your experience can meet those requirements. By providing detail in the cover letter, you help the recruiter to make the connection.