Not knowing where you live, it's hard to answer this question. My advice is to look up your state's local extension service site. They should have lots of information about what will grow during the fall/winter in your area.

I'm in the south, so I can grow quite a few greens during the winter, in fact, collards benefit from a winter freeze, but in more northern areas, that isn't possible without some sort of greenhouse or cold frame.

If you have a county extension service office, call them and they will send you literature. I know some people up north who have simple cold frames and grow greens and root crops all winter long. Some even have heated cold frames where they can grow must about anything.