Perhaps a good subtitle would be, "How do I earn a bit of money when I learn how to create a business letterhead in Word." Because you can always find ways to monetize your knowledge (that's what knowledge is for, isn't it?).
Personally I like to place my business address at the bottom of the page or the footer. To do this go to the floating bar and click on the button, 'Switch Between Header and Footer.' This will open a dotted box at the bottom of the document. You can type your office address here or anything you see fit for your letterhead. Again you can format the text by choosing the font, font size, color, align the text, etc.