What you need to know in order to create a mod

What you need to know in order to create a mod

if you're talking coding-language wise, you need to know/learn Java. Java is fairly easy to learn, you can just start by watching youtube tutorials, they help a lot, at least for beginners.

Android/IOS/PC or what do you mean?

https://www.youtube.com/watch?v=tD6MsMWIH-4
http://minecraft.gamepedia.com/Mods/Creating_mods

you should know java/eclipse wich isnt that easy

You should really learn Java first and then get started with the apis. For example use the Forge API

You would need to learn java. Theres actually a few YT series on how to create plugins.

At the first you need to know base of java.

if you will do a mod of just scripting and cool things, you would need only to know java, but if you want to create new models and etc you will need to know how to mess up with modeling softwares, generally blender probably