When writing a formal letter such as a certificate letter, you should start by addressing the person you are writing to by name i.e. Not 'to whom it may concern' etc. Then, keeping your language business-like and formal, request permission for the work you wish to do. Be specific about the company project work you are seeking and why you are qualified to complete it. List any relevant references and give your contact details in order for them to reply as promptly as possible. The letter should be dated and include an inside address (of the person to whom it is addressed) and should be either posted, or submitted by hand in an envelope.