You can align your logo by clicking any of the alignment buttons at the menu bar. Press the 'Enter' key on your keyboard and you can type in your business address or a slogan. You can format the text just as you would when you're creating a MS Word document. You can choose the font, font size, color, align the text and even add graphic lines.
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.