To add the trees, we'll go to Tools -> Vegetation Editor. This tool lends itself to being docked in the sidebar, along with the Terrain Editor, so let's dock it in the same window as the Properties tool or Terrain Editor tab (read here how to do this) and let the mouse button go, so it creates another tab for the Vegetation Editor.
First, we'll create a Group for the trees we'll add to our level so we can keep them separate from anything else we may want to add. Categories are just logical groups for your benefit. Organize your vegetation into similar groups that are easy for yourself or others to understand. i.e.: Trees, Grasses, Bushes, Underwater etc.
To do this, we click the Add Group button:
We'll double-click on the name of our new group and call it "Trees".
To get the pine tree, we'll click Add Object in the Vegetation Editor. This button is located right next to the Add Group button. Let's choose the one called simply pine.cgf. You can find several variations of this tree in objects -> natural -> trees -> pine.
In the Vegetation Editor, we can now expand our "Trees" group and you'll see that our pine tree is now located inside.
To 'paint' this tree on the terrain surface, we'll click the Paint button under this window and click where we want the tree to be:
If you want to place more trees of varying sizes, you can adjust the SizeVar value.
Size & SizeVar
Size defines what size you want the object be. A size of 1 means that the tree placed, will be at the exact same size as the artist who made it wants it to be (0.5 is half the size, 2 is double the original size).
SizeVar allows you to make slight variations of the model size, using the Size value as the base and applies the variations on top. SizeVar should be used with small values such as 0.1 -> 0.3 to add a slight variation between each painted down item.
It also looks a bit strange if all trees you place are rotated exactly the same way, making it quite obvious that you've used the same asset. To add a bit more variation, you can turn on RandomRotation. Tick the box next to it to make every new pine tree you place rotate randomly.
Another nice feature is that you can let vegetation objects move back and forth, as if they are swaying in the wind. This is called Bending. If we adjust the value for this in the Vegetation Editor, we'll see all pine trees we've already placed sway in the wind. Make sure not to overdo it though, as a high Bending value will make it seem like there's a hurricane blowing through your level. Unless you want to give it that impression, of course. For a gentle breeze, we'll give them a value of 5.
Now you can place some pine trees along the road and wherever else you want to place any.
The ground already has a grass material assigned to it, but it looks nicer if there is actually some grass on top of that. This we do in the same way as adding trees: in the Vegetation Editor. To make sure we can paint it separately from the pine trees, we'll click the Add Group button again and call our new Group "Grass". Now, we can add some grass. Click on our "grass" entry and click Add Object. Since the places where we can put grass are not very large, we're better off choosing a small patch of grass, like grass_small_normal (found in objects -> natural -> ground -> grass).
You may have noticed that in nature, there's rarely only grass somewhere, there are usually some flowers in between the grass. We'll add some to this group, so that we will paint the grass and the flowers at the same time. Click on our "grass" group again, click Add Object and look for ground_cover_flower_yellow_a (objects -> natural -> ground -> grass_tall). If you now select the "grass" group both of these vegetation assets will be selected and you can paint them onto your terrain at the same time.
When you get up close or go into the game to check it out, you may think the grass and flowers should probably be a bit smaller. Delete the grass and flowers you've painted by selecting the Grass group and clicking the Erase button. Now you can erase the grass and flowers without accidentally removing the trees as well.
Now make sure you still have the Grass group selected. Below the list, you can set the Size. Set this to 0.5. This will set the size for both the grass and the flowers.
Now you can safely paint the grass and flowers on any grassy surface you think it will grow.
It will now look a bit like this:
Next, we'll add a vehicle or two to be able to navigate our way through our level a bit faster.