Source: https://vrtoolkit.readme.io/docs

Created by - Giuse, for IATK, there are some critical components necessary that could be explained in VRTK.

This documentation might be up to date for users who use the Unity 2018 version, but the 2017 version is either difficult to access or doesn't exist.

The most important thing to do is understand VRTK SDK Manager Game Object, which allows VR simulation in Unity without a headset. SteamVR is fortunately very easily recognizable, and the plugin reacts to a headset almost instantaneously.

The VRTK SDK_MANAGER for how important it is, can't be found on the VRTK components to add. You must use search inside of an empty game object you create in the hierarchy. 

After adding the SDK manager you add VRTK Script components, which define how the controllers behave. There is a specific VRTK interact component you add to the controller for the input, and a specific VRTK component you add to the objects that the controller can be used on. From here, the skies the limit, but all of IATK is covered with these 2.5 components.