As others have effectively indicated, what goes in the covering letter depends upon what is already in the main application.
Philtaz's draft is fine if you've already provided all of the relevant information elsewhere. But if your application is little more than an outline c.v., the covering letter provides you the opportunity to expand upon it. For example, your application/c.v. might show that you previously worked as a 'customer service assistant' (with no detail as to what you actually did) but the job description calls for 'problem solving skills' and 'a good telephone manner'. In which case you can write "In my my previous employment, with J Bloggs Ltd, I was frequently called upon to deal with complex enquiries from customers, both face-to-face and by telephone. I enjoyed this part of the work, as it enabled me to exercise my strong problem-solving and communication skills".
Chris