When applying for a job, a cover letter looks like this:
It has a business letter format.
It has 3 paragraphs, and a professional closing/signature.
Paragraph 1: what position you are applying for, and how you found out about it
Para 2: why YOU are the ideal candidate for the position
Para 3: Ask for the interview: "My resume is enclosed for your review. I look forward to meeting with you to...."
Paragraph 2 is difficult to write.It should contain information that makes it clear that you have a solid understanding of what the company does and what the position entails. It should also show what experience you bring to the position that fits it with what they are trying to accomplish. Because of this, each cover letter should be personally written for the position that you are applying for..
For additional help, see gotresumebuilder.com which includes several coverletter templates.