Autonomous Arduino tank with seeedstudio motor shield and ping sensor.

So I need to have something that looks more like this?

int pinI1=8;//define I1 interface
int pinI2=11;//define I2 interface 
int speedpinA=9;//enable motor A
int pinI3=12;//define I3 interface 
int pinI4=13;//define I4 interface 
int speedpinB=10;//enable motor B
int speed =127;//define the speed of motor
 
void setup()
{
  // start serial port at 9600 bps:
  Serial.begin(9600);
  
  pinMode(pinI1,OUTPUT);
  pinMode(pinI2,OUTPUT);
  pinMode(speedpinA,OUTPUT);
  pinMode(pinI3,OUTPUT);
  pinMode(pinI4,OUTPUT);
  pinMode(speedpinB,OUTPUT);
}

And something similar to this at the end of the script, to tell the motors to move according to what the ping sensor reads.

 ; // wait for serial port to connect. Needed for Leonardo only
  }

  pinMode(2, INPUT);   // digital sensor is on digital pin 2
  establishContact();  // send a byte to establish contact until receiver responds 
}

void loop()
{
  // if we get a valid byte, read analog ins:
  if (Serial.available() > 0) {
    // get incoming byte:
    inByte = Serial.read();
    // read first analog input, divide by 4 to make the range 0-255:
    firstSensor = analogRead(A0)/4;
    // delay 10ms to let the ADC recover:
    delay(10);
    // read second analog input, divide by 4 to make the range 0-255:
    secondSensor = analogRead(1)/4;
    // read  switch, map it to 0 or 255L
    thirdSensor = map(digitalRead(2), 0, 1, 0, 255);  
    // send sensor values:
    Serial.write(firstSensor);
    Serial.write(secondSensor);
    Serial.write(thirdSensor);               
  }
}

void establishContact() {
  while (Serial.available() <= 0) {
    Serial.print('A');   // send a capital A
    delay(300);
  }
}

This is part of one of the examples in communications