The last thing you need before you can link everything you've downloaded to Unity is the Unity OUYA plugin. This can be downloaded directly from the developers at https://github.com/ouya/ouya-unity-plugin. Perform the following steps to install the plugin:
Click on the button on the page that says Download ZIP and put it in a location that's easy to find. When it has downloaded, unzip the archive and open Unity.
In the Unity window, navigate to File | Open Project…, browse the unzipped folder, and click on Open. On Mac OS, you may need to click on Open Other… to access the folder's location.
Depending on the latest versions of Unity and the plugin, you may be prompted to upgrade the project to work with the latest version of Unity. If it does, then accept the prompt; if you don't receive the prompt, it will work fine as it is.
After opening the plugin files as a project, two new drop-down lists will appear on the top toolbar of Unity: OUYA...