About the Invoice panel
You work with invoices in TimeCache via its Invoices panel. Assuming you have an invoice file open, you can show the Invoices panel by either choosing View>Invoices, or choosing Show Invoice Panel from the popup menu that appears when you click the Invoice icon in the toolbar.

The Invoice panel displays a list of previously created invoices, and a total at bottom right for outstanding balances. You can affect what is displayed in the list by clicking the checkmark to the left of any invoice you do not want to appear in the list, and checking the Hide Marked checkbox above the list on the right side of the Invoices panel. If you want to restore invoice listings hidden in this manner, uncheck Hide Marked and then uncheck the invoice listings you want to display.

In the lower left of the Invoices panel there are buttons for creating a new invoice, deleting an existing invoice, and displaying an existing invoice from the list. There is also a "widget" button with a popup menu that lets you add or delete invoices, and create "balance forward" invoices, as well as produce reports of invoices and payments.

When the Invoice panel is frontmost, the menu bar includes an Invoice menu to the left of the Window menu, which also gives you access to the Invoice panel's functionality.