Oculus Integration is the official SDK from Oculus and provides a comprehensive way to develop for hardware produced by Oculus, however the SDK can also be used on other supported platforms as well. The Oculus Integration package can be obtained from the Unity Asset Store.
Go to the Unity Asset Store by selecting
Main Menu -> Window -> Asset Store or pressing
CTRL + 9 and search for
Oculus Integration. Alternatively, click this direct link to Oculus Integration on the Unity Asset Store. Download and import the Oculus Integration Unity Asset into your project.