Asset Packages (with the file format of .unitypackage) are a commonly used way of distributing Unity projects to other users. When working with peripherals that have their own SDKs (eg. Oculus), you may be asked to download and import one of these packages.

Importing a .unitypackage

To import a package, go to the Unity menu bar and click on Assets > Import Package > Custom Package..., then navigate to the .unitypackage file in the File Browser that appears.