When applying for a job you will most likely need a one page cover letter (unless stated otherwise), and it needs to be targeted to the job or internship you're applying for. This is where you highlight what you have to offer, and how it matches what they are looking for.
It's also an opportunity for you to connect with a potential employer and explain why you are:
- interested in the position
- a good fit for the company, that shows you've researched them
- will add value to them