Well, simple you memorize which game you first played if you can as youngster (a child) or you can mention what type of game you played first online when you got your PC and how it all started in your gaming experience.
Let's start:
Mine is Metal Gear Solid, when i was young, my dad had bought the PS2 and the game itself and after work he used to come and play it and i used to watch him, later on after a month i started playing it, i didn't care what they are saying, i just wanted to play haha. Moreover years passed and at the age of 14, i started playing it again and decided to focus more on the story line, playing all Metal Gear series and it was pretty damn interesting and fun.
As for the PC:
It was Combat Arms, my friend's mum decided to install it on my PC since i didn't know how at that time haha, and later on me and my brother used to share the PC and play it, to tell you the truth we mostly fought to get the possesion of the PC all day to play the game. After some time, i made like 2 or 3 years playing the game. I surfed/looked into more the internet and started knowing how to install/download games later on and i moved on some other online games mostly FPS.