Functional programming, Scala map and fold left

What are some good tutorials on fold left?

Original question, restored from deletion to provide context for other answers:

I am trying to implement a method for finding the boudning box of rectangle, circle, location and the group which all extends Shape. Group is basically an array of Shapes

abstract class Shape  
case class Rectangle(width: Int, height: Int) extends Shape  
case class Location(x: Int, y: Int, shape: Shape) extends Shape  
case class Circle(radius: Int) extends Shape  
case class Group(shape: Shape*) extends Shape  

I got the bounding box computed for all three except the Group one. So now for the bounding box method I know I should be using map and fold left for Group, but I just can't find out the exact syntax of creating it.

object BoundingBox {  
  def boundingBox(s: Shape): Location = s match {  
    case Circle(c)=>   
      new Location(-c,-c,s)  
    case Rectangle(_, _) =>  
      new Location(0, 0, s)  
    case Location(x, y, shape) => {  
      val b = boundingBox(shape)  
      Location(x + b.x, y + b.y, b.shape)  
    }  
    case Group(shapes @ _*) =>  ( /: shapes) { } // i dont know how to proceed here.
  }
}

Group bounding box is basically the smallest bounding box with all the shapes enclosed.