Creating a new project
First of all, you'll need to create a new Unity Project (in my case, I named it Fungus3D).
Importing the Standard Assets
From the menu Assets > Import Package, import the following packages:
Note that some additional packages will be added, for instance Utility.
Open the Asset Store (Window > Asset Store), search for Fungus and download it.
You can also download the plugin from the browser (Unity3D will be opened and the download process will start).
Import just Fungus (not Fungus Examples).
You are now ready to create a scene prototype.