A writing agency - a good one for that matter - has asked me to send in a CV (which they said wouldn't matter if it's not that extensive, which it won't be) and a cover letter.

She recommended that I include what I've written, am writing etc., but can anyone with experience in such matters please give me a guiding hand? I'm young (which I told them, and they didn't mind) but that means I haven't got much experience with writing cover letters and the like.

Please help
Thanks for your time