For more elaborate scenery, select the Blueprints tab bottom right. Select the Trees option, choose what manner of bark-based beings you want, and place them as you wish. Skip back to the Terrain tab and in the Terrain sub-menu select the “non-walk” option. Here you select all the areas players can’t go to. Paint your lake and hills to prevent players wandering off. Then select File > Bake from the top bar to let your PC have a little think about what it all means.