Each winter the cold temperatures can burn plants. The evidence of frost burn are obvious and show immediately to a few days or weeks after the damage has happened. You will see this as dead tips of soft new growth, dead wood on older plant parts, fallen leaves that drop off after the coldest temperatures, etc. The best thing to do if you see frost damage on your plants is NOTHING right now. Those dead parts of the plants will help insulate the live parts of the plant and if you prune them off now, new tender areas will be exposed and you will likely have damage again on these newly cut areas, causing further die back. The dead parts from frost injury act as insulation to help protect the plant from further frost damage. You can prune these areas off after frosts are gone, later in spring. A bonus for waiting is that you can easily see dead growth at that later time. If you wish, you can still cover tender plants with a frost cloth, (even a sheet will work), during the coldest times and remove the cover in the day after those very low temperatures are done. Tender plants include citrus (although some are very hardy, like kumquats, mandarin oranges, etc.) Brugmansia, and any soft tipped new growth that did not harden off before the frosts came and grew late in the fall, early winter season. There are many other plants that are tender, this is only a brief guide. Do not feed these plants now. If dry, water them, but no water is necessary if they are in moist rain soaked ground. Spring is coming and you can then access the damage from frost more easily later as new growth begins below the dead parts. With hardy plants that had new soft growth burned, do not worry about them. They have hardiness built into their genes and will survive, only their late growth that was too soft for the cold, will have been damaged.
It is too soon to fertilize, wait until later. One possible exception are spring bulbs like daffodils, narcissus. They are making growth now, either root or top growth and some early types (paperwhites, etc) may be blooming as well. You can lightly feed these and any other winter growing bulbs with an all purpose food, taking care to not use a high nitrogen fertilizer. Bulbs tend to like more phosphorus and potash in their feeding. A light feeding now will promote stronger growth and perhaps better flowers, and will feed the bulb after bloom as it gathers strength to go dormant again later in spring. (you are making flower buds for next year if you feed them as they grow now).