To turn over a creature means to physically turn the card over. If the result is a face-down card, it's a colorless 2/2 creature, the same as one would get from using the morph ability. Turning a face-down card over results in it being turned face up. Any abilities that trigger when it's turned face up will work. Turning a double-faced card over is the same as transforming it. Any abilities that trigger when you transform it will work. Turning a combined host/augment creature over will result in a big colorless 2/2 creature represented by two cards. Turning a melded creature over will result in the two cards breaking apart and forming two separate creatures, but they'll probably just get right back together. Turning B.F.M. (Big Furry Monster) over is the same as turning a combined creature over.