Following is the template of writing a memorandum:
This will inform the addressee as to who sends the memo.
This is for whom the memorandum is written for.
Mention the reason of writing the memo in the first paragraph. For instance, there could be a memo sent to all the staffs of a company regarding the changes made in the company working hours. Management can also send memo about any visitors arriving at the company.
Finally, when you are ending the memo, close it with date of the event. Memorandum is also used as a legal document.