A genital massage is not, contrary to popular belief, an elaborate wank. It can be performed on both men and woman and helps to stimulate circulation in the area, helping to relieve blockages and increase flow. It can really help to relax you, giving you a greater quality of sleep at night and leaving you refreshed the next day. If this is something you're interested in, your partner should ideally have some experience in it, to ensure you get the best genital massage possible.
This should go without saying, but if you are looking for a genital massage it is best to clean up the area thoroughly. Spend a good, long time in the shower, keeping the water warm and have plenty of soap to hand. Make sure you clean every inch of skin there, and if you have foreskin roll it back to clean underneath it.
The massage uses slowly, sensitive touches to begin with, in order to warm up the area. Pressure will then be applied in circular massaging movements to the necessary areas in order to provide a thorough massage. Your partner might choose to warm some special massage oil to apply to the area, in order to help their hands slide more easily and give a deep, relaxing massage. Don't worry if you feel aroused and excited by the sensations - this is normal and the less time you spend worrying about it, the more relaxed you will be and the greater effect the massage will have.
While a genital massage is a very intimate thing, your partner may not want you to touch them while they are doing it. They will want to make sure you receive the massage you deserve, and so that any distractions, such as you touch them, may take away from your experience. Respect their wishes first and you will be sure to receive a great massage.