To complete this milestone, you will need to do several things.
Fist start by cleaning the rubble. This is a rectangle located at the bottom left of the game (press 1 on the keyboard). It will take about 20 minutes with 2 or 3 villagers. Then you will need to heat up the Cooking Pit. Put a villager onto of the pile of rocks your villager just made (at the bottom of the bridge), he will put it in the fire. Wait a little bit and the rock will become red. Take it out of the fire.
You will need four of those rocks. To guaranty your success you will need at lease 3 villagers. Each time a villager takes a warm rock out of the fire an other rock as to be put in. If you are not fast enough, the rocks will disappear.
When this done put one of your villager on the big leaf tree at left of the bridge.
That is all now you can shake the trees and get those giant yellow fruit. The villager will cook them and it will give 4 unit of food.