Level Design with vuforia

Hey guys I am a beginner in unity and vuforia. I am looking for the answers of following two questions -

1. How to come to know if image target has been detected in script ?

2 .

I have created basic apps with Vuforia. Now I want to make something serious but don't know how to go further.In this video at 1:00 they show a game getting activated after detecting the Mac donald's image .I want to create something similar.

Till now where I have reached is - I have detected the image , made all the objects in the game as child of image target(is their a better way for this?) ,add the ability to scale it and rotate it.

But how to make it playable I am not able to understand .Is their a way to detect collisions ? make player move away from marker?any specific api's I can refer.

 

What you're asking really isn't specific to Vuforia but basic Unity, I'd suggest this as a place start:

https://unity3d.com/learn/tutorials