It's a little bit different than the link though:
1. Create a new camera:
var happyCam = new FlxCamera(50, 50, 300, 300, 0);
2. Add it to the game's cameras:
FlxG.cameras.add(happyCam);
3. Change the camera your sprite is using:
sprite.camera = happyCam;
It can be a lot more complex than that (multiple cameras and so on), but this is the basic concept.