Traders are better off NOT using documents like LOI, ICPO, FCO, etc. Even if and when they rarely are used in internal trades, on a restricted level within specific industries, they have no legal or customary basis in International Trade whatsoever. In fact the presence of many of these terms are considered to be signs of Advance Fee Fraud, by knowledgeable players and law enforcement.
After you have written down the date, you can move on to the body paragraph that contains your intention to apply for job. Things you would state include your objective of joining the company? How can you enhance company's productivity? What is your previous experience in the field you are applying for? What is your academic background and how it can help you in your job? Lastly you can list down basic skills and experiences that you have attained from previous jobs, if any.