Difference between FXS and FXO

His i would like to know witch interface is connect to my phone operator.

FXS device is the handset.
The handset connected directly to the telephony card is an FXS device.

FXO is the analog line comming from the telecom that gets connected either to an hanset or PBX. FXO provides outbound dialling directly through the telecom provider.

The signallng type of FXS device is FXO and vice versa.

When a call comes on the FXO line it does an FXS signalling for ringing the handset.
When you pickup the handset the hanset does an FXO signalling to get a dial tone.
The FXO signalling is also used to send DTMF if I am not wrong.