In SpriteKit a Sprite is represented by the SKSpriteNode class (which inherits from SKNode).

First of all create a new Xcode Project based on the SpriteKit template as described in Your First SpriteKit Game.

Creating a Sprite

Now you can create a SKSpriteNode using an image loaded into the Assets.xcassets folder.

let spaceship = SKSpriteNode(imageNamed: "Spaceship")

Spaceship is the name of the image item into the Assets.xcassets.

After the sprite has been created you can add it to your scene (or to any other node).

Open GameScene.swift, remove all its content and add the following

class GameScene: SKScene {
    override func didMoveToView(view: SKView) {
        let enemy = SKSpriteNode(imageNamed: "Spaceship")
        enemy.position = CGPoint(x:self.frame.midX, y:self.frame.midY)
        self.addChild(enemy)
    }
}

Now press CMD + R in Xcode to launch the Simulator.

You can subclass SKSpriteNode and define your own type of sprite.

class Hero: SKSpriteNode {
    //Use a convenience init when you want to hard code values
    convenience init() {
        let texture = SKTexture(imageNamed: "Hero")
        self.init(texture: texture, color: .clearColor(), size: texture.size())
    }

    //We need to override this to allow for class to work in SpriteKit Scene Builder
    required init?(coder aDecoder: NSCoder) {
        super.init(coder:aDecoder)
    }

    //Override this to allow Hero to have access all convenience init methods
    override init(texture: SKTexture?, color: UIColor, size: CGSize) 
    {
        super.init(texture: texture, color: color, size: size)
    }
}