Unity engine basic question(C#)

1. What is the role of the Sphere collider on the Slingshot object?
2. What is the purpose of OnMouseEnter(), OnMouseExit()?
3. How do you read from the left mouse button? The right mouse button?
4. Describe the basic set of steps to read a mouse click, continue to respond to the player (dont halt updates) and then figure out when the mouse is released
5. What is the purpose of Rigidbody.Sleep()
6. How does Lerp work?