I read the tutorial but couldn't understand it. Well Anyway I tried it the best I could understand and what I end up with is a flat surface on the ground with a mortar texture in an oval shape with concrete around it. Now if I prone a little bit away I can see it under the map.

What exactly am I supposed to do

to make a hole select your terrain and press v to bring your vertices. Select a vertice and drag it down. keep doing this with as many vertices as necessary.
press the spacebar to duplicate the terrain patch and then select the crater texture.

You could do that...in a few hours. Apply a patch and hit "y", then hold Alt and click. Have fun.