Setup

1. Create an empty gameobject. (GameObject -> Create Empty) You can also use an existing gameobject.
2. Name your new gameobject "Gpu Grass Manger" or anything else you want.
3. Add the "Gpu Grass Manager" componet to your gameobject. (Click "Add Component" and select "Gpu Grass Manager")
4. Select your grass manager gameobject and in the inspector then select the "Terrains" tab and click "Add Active Terrains". This will add the active terrains in the scene to the manager.
5. In the grass manager inspector select the "Settings" tab and make sure your camera is set in the "Main Camera" field.

 

Adding Grass (or other objects)

1. Select the foliage tab in the Gpu Grass Manager inspector and the "LODs" sub-tab.
2. Click the "add" button.
3. Set the "mesh" and "texture" fields.
4. Set the name for the object in the "Settings" sub-tab.
5. Make sure the other settings are correct.
6. Repeat steps 1 - 5 for more objects.