Connect gearmotor with Encoder attached to Motor shield?

I am trying to connect this product Pololu - 378:1 Metal Gearmotor 25Dx70L mm LP 6V with 48 CPR Encoder (No End Cap)
To the Arduino Motor Shield Rev3.
So far I have connected the following

Encoder ----> Shield
Red Positive terminal of Channel A
Black Negative Terminal of Channel A
Green Gnd pin on Arduino (or breadboard)
Blue 5V pin on Arduino (or on breadboard)
Yellow No Idea
White No Idea

I don't know where to connect the "Encoder A output" and "Encoder B output" on the Arduino.
I'm thinking maybe the PWM, but there's only one for Channel A (pin 3)
Or can I use Digital Pins 5 and 6?

Thank you.

Encoder outputs should go to interrupt pins, they will change rapidly and are best handled by
an ISR (there are many many examples out there). Which Arduino do you have?

I have an Arduino Uno, and a Motor Rev3 shield attached to it.

Yellow No Idea
White No Idea

The yellow and white wires are the A and B encoder outputs, respectively, as described on the Pololu product page you linked. They can be connected to interrupt pins or input pins, with varying degrees of performance.

Any of the quadrature encoder libraries should work, but this one is good.

Thank you, I'll do more research on interrupt pins and how to utilize them.