4x4x4 EastSheen - What kind of piece is this?

[panda100123]

I know where it goes, but why does it look different on each side? Maybe this link can help: http://imgur.com/TXtbDRt
How does it go? Does the open-side go besides a certain color? My friend let me borrow it and it all fell apart, I really would like to put it together.

 

[Toddyt1]

It's an internal edge. Whenever I assembled mine I just put it either way.