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.
That's how to create a business letterhead in Word. Now, how do you monetize this new_found knowledge? Offer to your community a letterhead printing service. You can offer to design a logo and print the letterhead. Don't know how to design? Outsource it and then mark it up. Then go to a printing press, get a quotation to print letterheads and then mark it up. But don't mark it up too much. The point is to get as many clients as possible even with a small profits. Several small profits will always add up to big profits.