its a lot easier doing it then reading it, you got skype? I can show you its super easy
1)go to view go to new guide layout set gutters to 0 and columns and rows to 2
2)select rectangular marquee tool
3)drag from the top left to bottom middle(the guide should automatically lock the marquee tool onto the middle when you get near it)
4)duplicate the layer
5)select the entire image(ctrl a)
6)press ctrl t(free transform)
7)right click it and click flip horizontally