How do you write a cover letter to a publishing company?

Last year, I completed my first novel. For awhile it just sat on my computer until recently my father told me that he knows someone in a publishing company. He gave me her number and a slip of paper that said I needed to write a cover letter, synopsis, and give a sample chapter. Now I have a few questions. I'm a little paranoid about being so young (I'm seventeen) and I don't know if my unedited draft is ready. My mom is getting on my *** about it and I'm wondering how to write a cover letter, and should a sample chapter be the first chapter or the most intense one? And can you submit it unedited? Will they be flexible and understanding that I'm young and go over it with me or should I wait to do it myself? (I won't edit content because I'll be too harsh). Any hints or sites that will give me a hand? Thank you!!!