It's probably not the first but I have two early memories of internet use. One was downloading the Monkey Island 2 demo and thinking the download screwed up because instead of a game all I got was this useless "zip" file.
The other is going to a webpage that had all the item IDs for Baldur's Gate console and hitting print and ending up with like 20 pages.
That "ZIP file" comment reminds me of the early 2000s when I tried to find cheat codes for Need for Speed: Porsche Unleashed and found a ton of symbols I couldn't reproduce on my keyboard. "You're crazy, there's no square or triangle key, who's writing this stuff?!"