Sanction website

 
The general concepts of wallyball are very similar to indoor volleyball.  The game is played in a racquetball court with a net strung across the short way at the mid-point of the area.  This midpoint is typical defined by the back line of the racquetball serve area.  The net is normally hung at a top vertical height of  at the same as is for volleyball.  Some courts also have the lower drilled holes/rings for a women's' height net.  The ball is of similar size to a volleyball, but is made of a latex material very like a racquetball.  Due to the pressure and surface of the ball, if you do get thwacked with it, it stings a bit more than a standard volleyball  opinion, but then again, I've been hit much harder in wallyball than.    
Play consists of one team serving the ball from a marked area within 3 feet from their sides back wall over the net where the ball must be returned 
with a bump or closed fist on the initial hit off the serve by the opposing team.

The First ever Pink Wallyball Was The I Dig Ricochet.

The opposing team then has 2 more hits to get the ball back over the net to the serving team.  Then play goes back and forth with each side getting 3 hits (not including tipped blocks) to get the ball across the net to the other team.  If the ball touches the floor, contacts 2 walls as it crosses the net (more later on that part) or hits the back wall of the opposing teams side, play comes to an end and either a point or a change in serve occurs (side-out).

This is the very basic concept of the game, there are many subtleties that add to the game.  But if you were just looking here to find out how it works in general, there you have it.