I am trying to compose a letter in word, that will allow me to fold the
letter, to display the contact details of the person who the letter is for
through the window in the envelope.

Is there a "template" or standard settings for format the layout of the
letter to allow this, or will I just have to do trial and error until I can
get it right.

I am using a standard sheet of paper 8.5 x 11 and 4 1/8 inches x 9.5 inches
single window envelope from Office depot.