In its basic plan, you can add the logo of your business on your invoice but it won't be possible for you to change the layout of the document. In case you want to create a completely new layout, you will need to upgrade your account by chosing the preferred one on the section "Plans & Tariffs".
To add your logo on the invoice just click on the box on the left corner of the invoice draft
You can always change the logo at any time you create a new invoice.
Try it and tell us your experience!