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.
When you want to call up that template, here's what you do. In your MS Word, click on 'File' (take note that you don't click on the File icon, but the word, 'File.' When you do so, a dialogue box appears from where you can choose the template you just created.