Oscillators have 4 pins, but only 3 pins are used:
+5V
GND
clock out
There are 3 round corners and one square (or pointy... I don't know how to call it). The non-round corner is pin1 and is the pin that is not used. Viewed from the top, upper left is +5V, lower right is GND (like any TTL device), upper right is clock signal. Please, get a diagram in google.
ATMEGA168 has 2 XTAL pins, XTAL1 (pin 9) and XTAL2 (pin 10).
I think if you connect pin 10 to GND and the clock output from oscillator to XTAL1 (pin 9), you have a clocked ATMEGA168.
Are you mounting a standalone Arduino on a breadboard? If you want the atmega168 work with Arduino, you need to supply more components than simply the clock...