As described in the getting started video, you can use "To Dos" to track tasks for your clients or just track completed services to be invoiced later.
To Dos, like the invoice and balance sheet view, is a client specific view. The To Do items you see will reflect the client selected in the left hand list.
In addition to the client selection on the left, the To Dos view has a filter bar under the view buttons. It is labeled with the word "Show" and has 2 filter groups.
The first group is to filter task by completed or not completed. If you want to see everything, click All. The second filter is for invoiced or non-invoiced services. Again, to see everything, click All. The selected filter options are highlighted.
You can add new To Dos by clicking the "New" button in the bottom bar, through the menu, or with the keyboard shortcut Cmd-N. You can double click on any field to change the value. To mark tasks as completed, click the checkbox to the left of the item.
To use the built in timer, click a To Do item and press "Start" from the bottom bar. You can stop and restart the timer as much as needed.
When you are ready to invoice your services, hold your shift key down, and click on all the items you would like to invoice. Once they are all highlighted, click "Invoice Selected" in the lower right corner of the window. This will open a new invoice in the invoice view.