The source code details the pins that should be used for which function.
However, looking at the numbers used, it looks like that source code is meant for the Arduino MEGA, not he Arduino UNO. You will need to modify the pin numbers for the ping sensors to work with the UNO.
The pins you should use are up to you, just make sure they match the code.
This is the bit that defines which pins to use for the ping sensors:
#define TRIGGER_PIN 47
#define ECHO_PIN_RIGHT 53
#define ECHO_PIN_CENTER 51
#define ECHO_PIN_LEFT 49
The motors are connected up using these pins:
//-- MOTOR A --
int ENA=5; //Connected to Arudino Pin 5(pwm)
int IN1=2; //Connected to Arudino Pin 2
int IN2=3; //Connected to Arudino Pin 3
//-- MOTOR B --
int IN3=4; //Connected to Arudino Pin 4
int IN4=7; //Connected to Arudino Pin 7
int ENB=6; //Connected to Arudino Pin 6(pwm)