The tournament will be 3v3, played on special tournament realms, just like Blizzard's own tourney. The qualifier rounds start on this coming Monday, June 9th, and run through the 22nd, and the top two teams in the qualifiers from each region, North America and Europe, will be flown out to Los Angeles for the final competition, live on July 19th. The cash money totals to $50,000, with the winning team taking home $25,000, the second-place team $12,500, and the third- and fourth-place teams $6,250 each.
If you are interested in registering, which is free, do it by June 8th, since that's when registration closes. You have to be 18 or over and a resident of the United States, Canada, France, Germany, Spain, Sweden, Belgium or United Kingdom to compete. Here are the registration links for the different regions: Europe, North America. For more on the CGS tournament see their rules and FAQ.