Video Tutorial HERE
Step 1: In the top-right corner, select your account name > Settings.
Step 2: Select Transactions. You have the ability to add tax rates, payment instructions, additional information and legal document templates. These are preset templates that you can apply in invoices, consignment, and other transactions.
Another thing you can do is to customize your invoice PDF. Go to Settings > PDF Templates > Transaction, where you can customize your invoice layout, font, font size, artwork caption, etc.