You may start the invoicing process for the use of an asset from it's related job. Start by using the selection checkbox next to the asset in it's assignment table.

Only assignments that are marked "Billable" will be available for selection.

Once all assets for invoicing are selected, then click the "Generate Invoice" button.

The invoices module will open in a tab in your browser, copying the details of the asset into a line item in the invoice.