Ive just seen a job advertised that sounds ideal for me, and when i phoned to enquire they said to send a cv and covering letter. i didnt want to appear a bit dim and ask the woman, but what exactly is a covering letter? im in my first and only job, which i was offered when i was still a student, so only had an interview for it, so dont have much experience of the job market.
any help much appreciated!

A covering letter is simply a letter that goes with the CV saying in effect "please find enclosed my CV".  People often put other relevant information in the letter eg why they are interested in the job, what they may be able to offer.  Also any other information eg if you are about to go on holiday and so wouldn't be available for an interview for a couple of weeks.

this might help. I use it with my students.

thanks very much, thats a great help. i'll get to work on it over the weekend.