From the Invoices Dashboard, click on the Create invoice button in the top right corner of the screen or the middle of the screen (if this is your first invoice ever).
Follow the series of onscreen steps to fill in important details including your account information, recipient, and invoice type.
Add/edit any of the text in the yellow highlighted fields to make your invoice as detailed as possible. Before you send, many sure you confirm your invoice settings by using the Settings panel on the right of the screen. There's also a handy notes section for you to use...you know, just in case.