Learn another OOP(Object Oriented Programming) Language first, I suggest you learn python - it was made to help non-programmers interact with their computer at a deeper level and is an amazingly powerful language - then move on to JavaScript - it is very accepting of bad code & it doesn’t have any concept of variable types - and then move on to Java. Java is a language for people who already have large amounts of experience in OOP, it was invented to address the shortfalls of another language C (and C++ and C#) and it was expected that people using java would most likely have come from a background of writing code in C. C is a very low level and non-beginner friendly language and java is extremely similar. Minecraft and Forge also have their own constraints that they put on modders, sometimes it’s like having to learn a whole other language ?. Start small and before you know it you’ll be writing your own mod.
if you’ve decided to go straight for java & modding, at least watch some videos or read some articles about Java. Not writing code in java just about the language. Then have a look at some Java 101 tutorials to understand the basic concepts and you’ll be ready attack modding with your shaky understanding.
TL;DR
Do your homework - read up on Java and Object Oriented Programming