The good brands of feeds add vitamins, minerals, calcium and grit to their mix, so it is an all-in-one feed, nothing extra needed. You can usually also buy chick feed with or without medication, which is primarily for preventing coccidiosis. Here in my part of Missouri those brands include Purina and
MannaPro. You can usually buy it as pellets or crumbles. There are usually some cheaper brands that leave out one or more of those ingredients.
At the MFA and some feed stores you can buy a mix of grains, ground or pulverized for wet mash. Those usually don't include vitamins, calcium, grit, or medication, so you would need to add those or provide them on the side.
If you mix your own you will want to do some research so that you know what's available, what's cost-effective, and what your chickens need. Layers tend to need more calcium, meat birds are meant to be fed more so they grow faster, etc.
However, in the summer, I keep a pan of food in the dry parts of their runs and let them pasture. "Pasture" doesn't actually mean they eat only greens, because they eat moving food, too. They are serious omnivores who will eat road kill, if you let them. They eat hardly any of their pan food in the summer, preferring to catch or find their own. In the winter I use a good brand of store-bought feed, plus selected table scraps, fodder when I have time and room to do it, and the occasional baked and cooled cabbage, squash, or root vegetable that went too soft for my table.
If there is a protracted period of icky weather and everyone seems in the doldrums, I add a handful of scratch, bird seed or red millet to their usual food. That usually cheers them right up!