In your mod setup class, you need to add this to your item registry function:
event.getRegistry().register(new FirstItem());
FirstItem will be replaced with the name of your item class in src/main/java/jgcodes/fluxmachines/items and your constructor name in that class (their names should be the same).
Also, textures are client side, and you put your texture in the data folder which is server side. Your redstone ingot PNG file should go into src/main/resources/assets/fluxmachines/textures/item.
Lastly, this is preference (I believe), but I’d name your Mod class to the name of your mod, like FluxMachines.java, it ModClass.java.
Remember, you still need a model, a class, and an optional recipe.
If you need more help, here is my git repo (it has some other stuff in it that need to be ignored, such as a GUI): https://github.com/IAmAFrenchFry/CadeMod
Hope this helps.