How to generate random platforms scattered throughout a view? Just like Doodle Jump

so I was going through Ray Wenderlich's tutorial on how to make a game like Mega Jump using Sprit Kit and Swift. http://ift.tt/1zXEPmv. So he is loading an already created Plist with patterns and positions of the stars and platforms. So every time you start the game you'll have platforms and stars always on the same position.

So I have to make this project but instead I'd like to have the platforms and stars scattered all around randomly throughout the GameScene (Just like in Doodle Jump!). So every time you start the game platforms and stars will be at different positions. Any ideas on how can I do this?