When you arrive at the first location (i.e. after you have been washed up on shore by the ship) you have to move to the left of the screen. You will be asked to bash through the sand wall. You will meet a fella who will tell you to go see something gruesome.
You find a pile of corpses. One is alive. This lass is Lulu. She runs away, you follow her. The first mission she gives is to build a room.
Pick up the stacks of planks dotted around the building she is standing in. Use them to fill up the gaps in the walls. There are 6 in total.
Then that is it. Bam. Achievement.