how to create a new item

ok so i know how to make the recipe for the item i want to make which is just iron armor fused with diamond armor to make an improved armor

what im lost on is how to create the actual item itself and how to apply the texture to said item 

This is what i have so far as a test

var recipes = require('recipes');
var items = require('items');
...
var UpgradedChestplateRecipe = recipes.create( {
result: UpgradedChestplate,
ingredients: {
I: items.Iron_Chestplate(1),
S: items.slime_ball(1),
D: items.Diamond_Chestplate(1)
},
shape: [ 'ISD' ]
} );
// add to server
var addedRecipe = server.addRecipe( UpgradedChestplateRecipe );