My husband has diabetes, and he recently step on a nail on his job, at this point his foot is swell up and white around the wound. How shoud I treat?

Nail in foot. It is very important that you take your husband to a physician . Stepping on a nail through a shoe on the job can cause an infection in a healthy person, usually pseudomonas bacteria which can get very nasty! being a diabetic makes matters much worse, especially if the nail punctures the bone! this can be very serious! your husband needs to be treated immediately with antibiotics.
Have it evaluated. Deep puncture wounds can be potentially dangerous as one may develop tetanus, or a number of other types of deep infections. If the wound was deep enough they may lead to bone infections. If you develop pain, redness, swelling or other signs of infection seek medical attention to get the proper care.
SEE A DR! Diabetes+puncture wound=a big problem if you try to treat it yourself. See your primary and a podiatrist.
See MD ASAP. See an md asap the possibility of infection or non healing wound is real. If he hasn't had a tetanus shot in 5 years he needs one.
See your doctor. Based on your information, your husband needs to have this evaluated, by your doctor, the er, somewhere. The diabetes could impair his wound healing and increase chance of infection, especially if he has diabetic neuropathy, poor circulation, or high blood sugars.