In the following section we will create a new level and Landscape terrain so that we have something to use the Grass Tool with.
Create a new level that uses the Default Template as a base.
Add a new Landscape Actor to the level by first clicking on the Landscape Tool icon and then clicking on the Create button to add the Landscape Actor to the level.
To help better show off the Grass Tool we are going to add a tiny bit of noise to our Landscape terrain so it's not completely flat.
To do this go to the Landscape Tools and under the Landscape Editor section click on the Sculpt Tool icon to expose the available tools then pick the Noise tool
from the tool list and set the following properties with the following values.
This gives us a brush that is big enough to effect the entire Landscape terrain at once.
Since we only want a very subtle effect we set the Tool Strength very low and add more intensity by painting more.
Making the Noise Scale bigger makes the noise look smoother and more natural when applied to the Landscape.
Position the Landscape Brush in the viewport so that it covers the entire Landscape terrain then click the Left Mouse Button 3 to 4 times to add some very subtle noise to the Landscape terrain.
When completed you should have something that looks similar to the following image.
The above modification to the Landscape was done purely for artistic reason to help better show how the Grass Tool worked. If you needed to or wanted to you could use the Grass Tools on a completely flat Landscape terrain.
Exit the Landscape Tools by clicking on the Place icon in the Modes panel.