You may want to record where you get your business from. If so, you can add sources from the 'Settings' tab in the menu.
Recording the sources can help you with your return on investment advertising so that you have a coherent list of what is working and where you get the most of your opportunities and clients from.
In order to add a source, type your source into the 'New Source' box then press 'Add Source'.
To delete a source, hit the red cross in line with the relevant source.