executing 3 functions Respectively !!

how i can execute multiple functions ??
i want to execute (Go1)firstly then (GO2) … etc
this is my script :

function Update () {
GO1(); // (( this way Does not work !! )))
GO2();
GO3();
}

function GO1(){
if(Tasadom.isHit0&&Tasadom1.isHit1){
transform.Translate(0,0,0.07*FWDspeed);
yield WaitForSeconds (3);
FWDspeed=0;
Tasadom.isHit0=false;
Tasadom1.isHit1=false;
}


}

Assuming GO2 and GO3 are coroutines like GO1, they will all be running simultaneously. I recommend reading up on coroutines in Unity docs. There are probably many ways to do what you want though. You could call GO2 at the end of GO1 (inside the GO1 function I mean) and then call GO3 at the end of GO2. Another approach is to use a simple state machine, something like this (pseudocode):

int state = 0;

function Update() {
    if (state == 0) {
        GO1();
    } else if (state == 1) {
        GO2();
    } // etc

function GO1() {
    // Do whatever
    yield WaitForSeconds(3);
    // End of function
    state = 1;
}

function GO2() {
    // Do whatever
    yield WaitForSeconds(3);
    // End of function
    state = 2;
}