Using MSP430G2553 to create a SPI communication with PGA116 mux

I am trying to use PGA116 multiplexer to select 4 signals and using msp430g2553 to select the channels .

I have trouble understanding which pin from the microcontroller is connected to the multiplexer to select the channels. I gone through the data sheet and connected the SCLK, MISO, MOSI between the two devices.

I also found the code from this link  http://www.argenox.com/library/msp430/ch9-msp430_spi.php

I connected everything as per design ,but i cant get the multiplexer to work....So please find a solution for my problem as soon as possible.

#include <msp430.h>

int main(void)

{

    WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT

    P1OUT |= BIT5;

    P1DIR |= BIT5;

    P1SEL = BIT1 | BIT2 | BIT4;

    P1SEL2 = BIT1 | BIT2 | BIT4;

    UCA0CTL1 = UCSWRST;

    UCA0CTL0 |= UCCKPH + UCMSB + UCMST + UCSYNC;  // 3-pin, 8-bit SPI master

    UCA0CTL1 |= UCSSEL_2;                     // SMCLK

    UCA0BR0 |= 0x02;                          // /2

    UCA0BR1 = 0;                              //

    UCA0MCTL = 0;                             // No modulation

    UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**

}