This achievement can be unlocked in Chapter 1 after being chased by the dog in the field. Following the path will lead you to a new area. Follow the path, go down the ledge and you will see a wheel and a bridge in front of you. Use the little brother (RT & RS) to move the wheel to lower the bridge. Once the bridge is lowered, use the big brother (LT & LS) to cross the bridge and pick up a sheep. Cross back over the bridge and put the sheep into the wheel; this will lower the bridge again. Use the big brother to cross the bridge again and pick up another sheep. This time after crossing the bridge take the left path. Drop down the ledge and take the sheep to the fire pit. Let go of LT to make the sheep black and the achievement will unlock.
The achievement can be seen in my video guide: