SKScene represents a single scene in a SpriteKit application. An SKScene is 'presented' into an SKView. SKSpriteNodes are added to the scene to implement the actual sprites.
Simple applications may have a single SKScene that contains all the SpriteKit content. More complex apps may have several SKScenes that are presented at different times (e.g. an opening scene to present the game options, a second scene to implement the game itself and a third scene to present the 'Game Over' results).