ViewController, his main role is what? I do not know his role. Ion-picker-cmp, when he is used, the source code to see is not too much to understand

Ionic Framework ionic-v3
1

ViewController, his main role is what? I do not know his role. Ion-picker-cmp, when he is used, the source code to see is not too much to understand.

2

What are you talking about? Can you provide a link to whatever has this ViewController?