[1.8.9] Why is my item not initializing?

So I'm new to mod development, and I'm following this tutorial, and I cant seem to figure out why the item isn't being initialized. I followed the code exactly as the video says, but the game just isnt initializing the item as far as i can tell.

This is the contents of my ModItems.java file:

package notrainbowsteve.mcap.init;

import net.minecraft.item.Item;

import net.minecraftforge.fml.common.registry.GameRegistry;

public class ModItems {

public static Item copper_ingot;

public static void init() {

copper_ingot = new Item().setUnlocalizedName("copper_ingot");

}

public static void register() {

registerItem(copper_ingot);

}

public static void registerItem(Item item) {

GameRegistry.registerItem(item, item.getUnlocalizedName().substring(5));

System.out.println("Registered Item: " + item.getUnlocalizedName().substring(5));

}

}

it might be worth noting that I'm not entirely sure what the .substring(5) part under registerItem actually means, specifically the number being used. I think I understand what the substring part means, but I'm not entirely sure on what the 5 means.

this is the contents of my main .java file (called MCAP.java):

package notrainbowsteve.mcap;

import net.minecraftforge.fml.common.Mod;

import net.minecraftforge.fml.common.SidedProxy;

import net.minecraftforge.fml.common.Mod.EventHandler;

import net.minecraftforge.fml.common.event.FMLInitializationEvent;

import net.minecraftforge.fml.common.event.FMLPostInitializationEvent;

import net.minecraftforge.fml.common.event.FMLPreInitializationEvent;

@Mod(modid = Reference.MODID, name = Reference.NAME, version = Reference.VERSION)

public class MCAP {

@SidedProxy(serverSide = Reference.SERVER_PROXY_CLASS, clientSide = Reference.CLIENT_PROXY_CLASS)

public static CommonProxy proxy;

@Mod.Instance("mcap")

public static MCAP instance;

@EventHandler()

public static void preInit(FMLPreInitializationEvent event) {

ModItems.init();

ModItems.register();

}

@EventHandler

public static void init(FMLInitializationEvent event) {

proxy.registerRenders();

}

@EventHandler

public static void postInit(FMLPostInitializationEvent event) {

}

}

if I need to give more info, im more than glad to do so if it means i can get this working.