If you're playing Java Edition of Minecraft, I would start by googling "Java coding" and familiarize yourself with the language.
Creating java mods without some editor will require intermediate knowledge for what you are looking for.
On top of that you will also have to familiarize yourself with forge or fabric as dependencies & other functionalities so you would have to learn one of those as well.
Java modding is definitely not entry level and will take some knowledge of the language and how to use a coding editor like Python for example.
For the items and loot however, data packs and some mod editors may be available to you, but to add new dimensions and new features I'm unsure of.
