Where to hook second SS slave select on MEGA2560 board

I have a MEGA2560 board. I am trying to work through an example in a book concerning the SPI bus. The board in the example in the book is a Arduino Uno, which has different pins than the MEGA2560. The example in the book uses two SS slave select pins on the Arduino Uno board--pins 10 and 9. I know pin 53 on my MEGA2560 board is my SS slave select pin. Where do I plug in the second SS slave select pin on my MEGA2560 board? Pin 50 is the MISO, Pin 51 is the MOSI, Pin 52 is the SCK. Pins 44,45,46 are the PWM pins. I don't know what pins 47,48, and 49 are? Where do I plug in my second SS slave select? Thanks!

Any digital pin can be a slave select, if not otherwise in use. You just write your program accordingly.

Thanks jremington.