Try to always get a contact name and send it specifically to that person. If that is not possible, “Dear Selection Committee” is appropriate.
The first paragraph should state what you are applying for and how you heard about the position. Bold the position title and number (if listed).
The middle paragraph(s) should take a few of the key qualifications listed in the job description and list some examples of where you have gained that experience.
The last paragraph should cover when you are available and how they can best reach you.
Somewhere in the cover letter mention why this is a good fit.