A viewing means to have an open casket. A visitation is when the body is in the casket (which may be open or closed) before the service so that friends and family may come to "visit." A visitation offers a chance for people to "pay their final respects" to the deceased.
Just as important, the visitation can be a time for family and friends to meet and console each other in a more informal setting than at the funeral. You can schedule a visitation for as little as half an hour on the day of the service, or it can last for several days before the service.
The visitation can be restricted to just close friends and family, or be open to the public. You can even have a combination of private and public hours.
Is there a special ceremony?
As part of the visitation, you can arrange a formal ceremony, an informal ceremony, or none at all. The formal ceremony might be a brief service with the saying of the rosary (for Catholics) or prayers for the dead led by a mourner or member of the clergy.
For those who are comfortable with it, an informal storytelling session can be a wonderful way to remember the person. The stories don't all have to be solemn, nor do they all have to show the person as a saint. We often love people as much for their flaws as for their strengths. Remember, too, that laughter is as much a sign of strong emotion as tears or anger. And if the person had a good sense of humor, there are bound to be some funny stories.
This sharing can be a rich and powerful experience. You might even want to tape record this event to listen to again later.