And by coincidence, you can get help on this very task through the British Council's Learn English Professionals site.
On entering the site, just click on the 'Work Skills' tab on the Main Menu bar which runs along the top of the page, just below the banner.
A drop down menu appears; choose J@M: English in the Workplace. Read about 'J@M, London's best known web design company'. Then click on 'Watch J@M now'.
From the menu, choose 'Episode 2: Applying for a Job'. This is an animated cartoon. One of the pictures shows you a sample job application letter. It will help you to do your homework!
And when you have finished, take time to explore other things in Learn English Professionals. Try, for instance, 'Downloads', then go to Podcasts. These are listening files that you can save to your computer - or even your 'telefonino' (mobile phone). Then you can listen to them as many times as you like.
After reading this and trying Learn English, please do write a short comment either on the Tag Board or in the comments section just below this article.