^ You're a new fan? I used to be freaking confused too, but not anymore.
Top line: Sooyoung --> Seohyun --> YoonA --> Yuri --> Hyoyeon
Middle line: Jessica --> Tiffany
Bottom line: Sunny --> Taeyeon
Rumored schedule:
June 19th – Teaser
June 22nd – Mp3 release
June 25tht – Full album release
June 27h – MBC Music Core Comeback Performance
Credit: http://snsdkorean.wordpress.com/