Here is an easy to refer mapping of Atmega 8 pins to Arduino.  Credit of this image goes to user called “System” on Arduino forum https://forum.arduino.cc/u/system/summary

The image has been taken from the post https://forum.arduino.cc/t/pwm-didnt-work-on-atmega8/248564

A neat and to the point image like this is rare on the internet. I have just put the image here as a mirror of the original to ensure availability.

To read more about how to use Atmega8 with arduino bootloader, see

Burning Arduino Bootloader to Atmega8 or other Atmega

Using Atmega8 or Atmega328p directly without using Arduino boards