one followed by 100 zeros

I started using Google search shortly after its launch in 1998. At the time, Alta Vista sometimes found what you wanted (and sometimes didn't), Yahoo still indexed sites by hand (and censored, so we were told), and the rest... I don't even remember, because quite frankly they sucked. I was teaching basic HTML classes to high school students, and one assignment was for them to compare search engines. People tended to use two or three and switch between them, depending on what they were looking for.

And then word went around about this search engine that was named after a number, and the number was named after the first couple of syllables that came out of a kid's mouth when his mathematician uncle asked him for a name. Any search engine with a moniker that massively nerdy was worth checking out.

What: the Google search engine.
When: since it was in beta, so 1998-ish.
Who: at first me, whoever told me about it, and whoever I told. It seems funny now, but I do remember being an enthusiastic word-of-mouth evangelist of it.
Where: on dial-up. Google's famously minimal search page was well-appreciated for that alone. I also liked how they repeated the letter "o" above all of the page numbers between 2 and n-2.
Why: It loaded quickly. It responded quickly. And, astonishing for 1998 but still appreciate now, you could actually find what you were looking for. Besides, the "I'm Feeling Lucky" button still makes me smile, even though I never use it.
How: lots of different ways, depending on what you want to know. It translates! It converts! It calculates! It maps! And so on.

Bonus: It's become so entrenched, so easy to use ('til the next thing comes along, but in my humble opinion that hasn't happened yet, bada boom bada Bing), that there's even "duh" parody sites.