Cover letters, accompany and introduce your resume. NEVER send a resume without one unless specifically stated not to send one. Below is a video giving you an overview of a quality cover letter.
The cover letter is an additional document to your resume, but make sure you do not duplicate exactly what is already on your resume. A well-written cover letter will make the employer want to read more and it will raise their interest in you as a possible candidate.Do not write a "generic" cover letter for various positions. It has to customized to each job or internship.Below are resources for writing good cover letters.
SU Writing Center (receive help in all areas of writing)