From TaskArtist Wiki

TaskArtist Installation

In order to install TaskArtist you have to download the dmg file and open it. You will find the application 'TaskArtist' and a symbolic link to your Applications folder. Simply drag the app to this folder.

Using the tutorial

If you would like to use the Tutorial file, copy it to your harddisk. TaskArtist creates reports in the directory your project file resides. The downloaded disk image is not writeable and therefore will prevent TaskArtist from creating any reports.