Materials are extremely simple to make! If you haven't already, make a .txt file named "materialList.txt" in your Content Pack Folder. Open it up. Here is an example of a material added. Please excuse the weirdness of it, testing if content creation works is rather boring so I start writing weird things.
Be careful to include all proper commas, semicolons, etc. One mistake and the item will not work properly.
recipe: (5), [potato, 5], [gold_nugget, 2];
This is the name of the item that will appear in game.
Registry Name Edit
This is used for textures as well as identification. Each item must have a unique registry name.
Stack Size Edit
How the item is crafted. The first element in this example "(5)," is the amount of CraftaTatos you will get in this crafting recipe. The next 2 elements are the requirements. in the example "[potato, 5]," potato is the item required to craft this item and the number is the amount of potatoes needed. "potato" is what the Potato item is registered under in vanilla minecraft. I believe registry names are found on the minecraft wiki.