First, install the application from the dmg package by dragging the application icon to your application folder.
At first launch, you will have to authenticate with your administration password to allow the application to mount volumes.
An black cat icon will be added to your status menu.
Clicking to the icon will search for NTFS volumes connected to your computer.
When search is complete, you will have a list of your available NTFS volumes. Just click on one of them to mount it.
You will have to eject the volume first if it has been automatically mounted by your system.
NTFS Mounter won't eject the volume by itself to avoid any other applications to crash if they
are accessing files on the volume.
Once you have ejected the volume, you can try to select it again from the menu.