What should the letter say? Comprehensive guide to writing an invitation letter for your US visa application, with free samples and tips.This is an overview of the steps required to apply for a visa. Keep reading our website for more detailed information, including how to book your medical exam. Full Name and Contact Information – The letter should begin with the host's full name, address, and contact details. You can download an invitation letter from a link in your acceptance notification email. If you are NOT PRESENTING, you MUST REGISTER for the meeting first. The NWL Occupational Health Service will send you an email invitation to complete your OH Questionnaire via an online system.