Hi , to add the vive tracker to your project you need:
1) Pair the tracker in SteamVR application.
2) In Unity3D project add SteamVR_TrackedObject script to the object you want attach to the tracker.
3) In SteamVR_TrackedObject pop-up menu "Index" choose "Device#" that correspond to your tracker. Th find the corresponding "Device#" run the app and select various "Device#" while program is running - until position and rotation of your object start changing according your tracker position/rotation.
Probably, there are better ways to find the appropriate "Device#" but I don't know them.