That section is good. There is two ways to do modding.
1.There is the easy way with Mcreator
If you want to use Mcreator for modding if you aren't too sure about coding a mod then I'd recommend starting there, you just click to make things happen like creating tools, armour, blocks and items is easy, you just set the stats, add the textures/create your own. While with dimensions, biomes and more it can create based on what the overworld, nether or end is like. You can find Mcreator here: https://mcreator.net/. You don't need a JDK for Mcreator though.
But if your fine with coding mods I'd recommend watching video tutorials on Youtube, but be sure to look for videos that cover the version your looking for of Minecraft, because if you don't want to see how to make mods for 1.15.2 but instead 1.12.2 then there is noticeable differences (things change between versions due to the modloader creators or Mojang) and modloaders to choose from.
If you are fine with learning how to code I'd recommend getting a JDK (Java Development Kit), the OpenJDK is probably best as Oracle (the company that owns/maintains Java) changed their rules so OpenJDK makes it easier to get started instead of needing to be a business or go through other means just to get a JDK (I think this is the right link: https://jdk.java.net/14/, just get the one for the Operating System you use)
The one thing to consider with modding is what Modloader you want to make for (Forge or Fabric) and what IDE (Integrated Development Environment, this is the application you will use to code) you want to use, the common ones are IntelliJ, Eclipse and Visual Studio Code (you do need a JDK for these and some Java plugins). Again I'd recommend using a Youtube tutorial to get started if your coding as they will give you an idea about this sort of stuff.
Good luck. I've tried a bit of modding (never completed a mod though) using MCreator and coding and it's not too bad, it takes a bit to get into it though.