Also is it necessary that additional packages be saved with my project folder each time I back it up to use on another computer? If the packages I need are already installed on the other computer can’t it just ’ read’ them? It just seems like a lot of files to be be backing up before even starting to build a new game.
To import additional assets from packages, use the Assets → Import Package… menu. Once you’ve imported it, you don’t need to keep a copy of the package, as its content are then in your project’s Assets/ folder; backing up the project backs up the stuff from the package too.
The Terrain Toolkit and the Public River project are zipped files that are not a unityasset file. You unzip the folder directly into your project (such as in Standard Assets, or its own folder). Then let Unity import the assets automatically and use them in your scene.
You DON’T do “import package” from the menu like you do with the other types of asset packages.
This confused me since there’s nothing to that affect on the Terrain Tools download page.
EDIT: This is ALL WRONG!
The original advice to import the unity package is absolutely correct.
The problem I was having with the Terrain Tools is that the unzip utility on my Mac was unzipping to the folders and not leaving the Unity package in place. I unzipped with a different tool and got the Unity package.
Sorry for the confusion and bad advice.