Back in my early high school years, I used to play a lot and I mean a lot of Minecraft.

First off, what is modded Minecraft. Well, basically there is are files called mods, that are add-ons to the basic Minecraft realm. You can add hundreds or 2, however many you want. Because Minecraft was written in the popular coding language Java, it is quite easy to make a so-called mod that modifies the gameplay in the original game.
There are many ways of playing modded Minecraft. There is what the community calls “Vanilla” Minecraft which is the untouched original game and there is “modded”. Vanilla is where you double click on the Minecraft logo on your desktop and it opens up a launcher where you can select the version of Minecraft and your account and boot it up. One of the easiest ways to load modded Minecraft is by downloading a modded Minecraft client, such as Feed The Beast or the popular Tekkit. These two third-party launchers allow you to loads dozens of mods pre-packaged together for you fast-forwarding the modded process.

I got into modded Minecraft from watching a Twitch stream when I was 13 or so, I think I actually played modded before I played vanilla seriously. I became fascinated with it because it allowed my creativity to be pushed exponentially compared to the vanilla versions. There was so much new stuff to do and learn, I became infatuated.
I hope I tapped into either an old memory of yours or maybe inspired to get into and try modded Minecraft I personally got lost in the game for hundreds of hours.