Take a look at page 9 in the owners manual!
CONTROLS AND FUNCTIONS
Rear panel
1 CD input jacks
Used to connect a CD player (see page 9).
2 PHONO jacks and GND terminal
Used to connect a turntable that uses an MM cartridge,
and to ground the terminal (see page 9).
3 Audio input/output jacks
Used to connect external components, such as a tuner,
etc (see page 9).
4 DIGITAL (OPTICAL) jack
Used to connect a component with a digital optical
output (see page 9).
5 DIGITAL (COAXIAL) jack
Used to connect a component with a digital coaxial
out