Creating a Basic Item

First of all, copy the myItems.png file into the mod's texture directory. Next, create a file in your mod's item directory and call it stoneStick.js. Add the following contents to it:

name = "stoneStick";
id = config.getItemId("stoneStickId");
displayName = "Stone Stick";
addToCreative = true;
creativeTab = "materials";

textureFile = "myItems.png";
textureIndex = 0;

Then, open the mod.js file and add the following lines to it:
config.addItemIdProperty("stoneStickId", 6000);
mod.addItem("stoneStick.js", "normal");

That's it. You find the item in the materials tab of the creative inventory.