Flow of my program

Processing
4

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Do you want to press only one time on the mouse and then it plays every scene automatically or you want to press on the mouse everytime you want to go to the next one?

I think you mean the second one so I’ll answer that one.
In order to do that you just need to have a variable to keep track on wich scen you are at.

int currentScene;

void setup() {
  size(500,500);
  currentScene = 0;
}

void draw() {

}

void ball1() {
...
}

void ball2() {
...
}

void ball3() {
...
}

void playScene(int nb) {
 if (nb ==1) {
   ball1();
 }

 if (nb ==2) {
   ball2();
 }

 if (nb ==3) {
   ball3();
 }
}

void mouseClicked() {
  currentScene++;
  if (currentScene > 3) {
    currentScene = 1;
  }
  playScene(currentScene);
}