Install the product. Target the Carrara application folder itself and not a subfolder in Carrara.
For example, if this is your Carrara folder path:
C:\Program Files\DAZ 3D\Carrara8
Then the Carrara8 folder above should be the target folder indicated in the installer.
In Carrara, you'll need to add the folder to the browser. The readme tells you where the files for the product will be.
You can also add the content (.car & .obj) to the browser with the 'Add Folder' button in the upper right corner.
If this is your Carrara 8 install path:
Program Files\DAZ 3D\Carrara 8
Then in the browser, click the 'Objects Tab.'
In the upper right corner of the browser, click the icon that looks like a piece of paper. You'll see a menu appear.
Click 'Add Folder.'
Browse to your Carrara 8 folder and within there to this folder:
Then choose 'Plants' as the type of content.
In Object menu in browser, scroll down to 'ReplicatorGrass' and select it.
Now look to the larger pane in the Browser.
You should see several plant choices. Try one of them, like Grass 2.