ATmega8 USB programmer
The programmer you have programs the ATmega8 through the ISP interface on the device. Here is the pinout of your programmer:



You can see the circles and the one square? The square denotes the 1st pin, or MOSI.

I think I found the right datasheet to your ATmega8 MCU, please double check the datasheet for the MCU that you have. 

Extracted from the ATmega8/ATmega8L datasheet found here:
ATmega8 datasheet



You can see that pin 19 (PB5) is the SCK pin. Pin 18 is MISO, 17 is MOSI, 1 is RESET. These are the pins that connect to the appropriate ISP pins that you can see in the first picture above. 

So your overall system will be like this:


Have the ATmega8 powered from a reliable DC 5V power source
Ensure the ATmega8 is grounded
Connect the pins of the ISP programmer to the appropriate pins on the ATmega8
Pull up resistor (~10k) on the RESET pin.


This is all you should need to get the programmer to talk to your MCU using your computer.

Best of Luck.