// Below two values are variables that I will use later
float xPosition = 0;
float yPosition;
float xSpeed = 3;
float ySpeed = 3;

void setup(){
  size(450,350);
  smooth();
  noStroke();
  yPosition = height/2;
}

void draw(){
  background(0);

  // checks to see if ball position is larger than width of sketch
  if(xPosition>width){
    xSpeed = -3; 
  }

  // checks to see if ball position is smaller than 0 (left wall)
  if(xPosition<0){
    xSpeed = 3; 
  }

  fill(0,20,220);
  ellipse(xPosition,yPosition,50,50);
  // The below line says that the value of xPosition will grow by 2 every frame
  xPosition += xSpeed; 
}