The game will be available worldwide on July 27th. As announced 2 years ago, there are going to be 3 chapters in total. The first one to be released this July will be "Wings of Liberty", Terrans' campaign, with 29 single player missions to play. Players can choose to play as Zergs and Protoss in the multiplayer component only.
The release date for the other two chapters, "Heart of the Swarm - Zerg" and "Legacy of the Void - Protoss" is not available at the moment.
Time to get an upgrade for my PC. ^^
Information is from Gamespot. Images are from this and this previous posting.