How do I make actors fly in from off screen?

hamzawesome

I've started making my game and right now, the only actor that the player can move is a ball, which bounces up whenever it is touched, and I want it to be the only actor that the player can move. However, I'm trying to add spikes that come from off-screen (only the left and right sides of the screen) and fly horizontally to the other side of the screen and disappear off-screen. They need to be avoided by the ball. I've added the spike as an actor, but how do I make it so that it flies into the screen at random time intervals and from random Y positions from the left and right sides of the screen? Once they collide with the main actor (the ball), the game is over.