Invoices are primarily comprised of Items, which are also the key components of Projects and Quotes. This means you can move interchangeably between these three states of work without any manual conversion.
Items are exactly the same across Quotes, Projects and Invoices, meaning at any time, any one of these documents could be turned into another. For instance, you can entirely plan your Project from the Quote, and then turn that Quote into a Project complete with deadlines and to-do Items. You could also progressively Invoice your client based on a timeframe of Project activity.
While details such as Labour(In)$ rate can be specified in the interface, you will ultimately have the choice as to what information is displayed in the client copy.
To create an Invoice, hover over Invoices in the side-bar menu, then click the "Add+" button:
From here, you'll have the option to create your Invoice based on existing project data, from scratch, from a Quote, or from an Invoice Template:
The default Layout options for your Invoices can be configured in the "Invoice Settings" section of your settings.
If you are creating your Invoice based on Project Data, keep in mind that you can choose to invoice for a specific portion of the Project. There are options for invoicing within a certain date range, or simply for Time Records that are as yet not invoiced for.
From here, the Invoice is broken up into a series of sections. You'll see contact details at first, followed by a description, and then items. These items work in much the same fashion as seen in your Project Details Page.
