At the end of Chapter 1-2 "ANOTHERLAND" you'll unlock your Magic Marker. This Achievement requires you to use the marker 25 times.
There's really no trick to this. You'll unlock very quickly during the normal course of the game; however, if you just can't wait, then you can unlock it on the first pillar of earth needed to clear your path in Chapter 1-3 "SEA OF SAND." Simply create and destroy the pillar over and over until the Achievement pops.