This is /give: /give @s diamond 4. If you do that, it will give you 4 diamonds. It’s basically giving yourself stuff using that command.
However, there are two downsides: /give @s iron_ingot You need to put the “_” in.
The next downside is it has different words then actually in real Minecraft. A good example is “Writable_ book” Instead of “Book and Quil.”
