To add your address to your store's contact us page and invoices:
Click on the menu Configuration > Store Settings > General Settings:
You will now see a screen with "Edit Settings". Click on the "Store" tab.
Scroll down to the field: "Address" and enter your stores address. This can be a PO box if you're a home business and don't wish to display a physical address.
Once entered, click the "save" button.
You can place the store address that you have created in any blog post, content page, or description automatically by using the [store_address] shortcode.