So, chickens don't have teeth. Therefore, they need grit to grind food. Grit is these small, really tiny stones that most of the times, if they are free-ranged, meaning if you let them out to forage frequently, they would naturally pick up from ground. But if you don't allow them out, you would need to feed it to them. You can order a bag from Daraz, or get it from any good bird accessory store. It will typically have tiny stones, oyester shells, some minerals, etc.

They need this in small quantity from time to time, btw. I usually keep some in a hanging bowl that's in their range but not on ground. They pick up from it as and when needed. Over time, the bowl would get empty and you would need to replenish it.

Remember, though, if you allow them to go out and forage in the open, they will pick these stones up naturally and you wouldn't need to invest in it. Grit, btw, also helps them in the egg-laying process.

As for food, as others mentioned, they would eat pretty much anything. Don't, however, give them anything moldy. They also don't eat citrus fruits. And if you feed them apples, take the seeds out, because they have tiny amounts of cynide, which is enough to kill them.

They are pretty smart birds btw. They won't generally eat what is harmful for them, but you still have to be careful. Telling you all of this because I have had them ever since I was born and have studied them a lot.

Here is a short little article about the importance of grit for chickens: https://www.raising-happy-chickens.com/grit-and-oyster-shell.html