Hello Man! I'm a mod maker myself too! So you wanna make a mod? Well, heres some basics of how mods are made
-A mod is something that is short of modification which modifies your minecraft game! But how? Minecraft is made in a specific way, running on a certain engine! Thats the very hard part of creating a GAME but to add items and blocks and mobs and more to the game is abit more simple! It is made by adding files called .class files, or .java files these files are made and put to the game and your game "minecraft" reads it and puts it in the game, but how do you make these files? Theres a thing called coding, it is a series of "codes" or "words" put into a certain way so that whatever you want to put this "code" into can read it. Since minecraft runs on a Java - based engine you have to make it on a "Java" way so you would Require JAVA PROGRAMMING KNOWLEDGE, but if you don't, then you can simply find some posts on minecraft forums that are tutorials!
PLEASE NOTE - Doing something like this takes patience and practice, don't expect to make an awesome thing just yet! The makers of the Godzilla has probably years of experience! If I were to make something like the godzilla then it might take about 1 - 3 weeks for MEH!