You create the mask by drawing it in the Mask interface which is launched by the Edit Mask button in the properties panel.
For drawing, you have two options: Draw and Erase. The brush size slider lets you change your brush size for either operation.
If the Input port is connected to another node, a 2D representation of that terrains is shown in the background as a guide. This is optional, as the Input port only provides a drawing guide and does not affect the actual mask.
|Blur||The amount of blurring to apply.|
|Iterations||The number of times the blur is applied. Higher values give more varied softness at the expense of processing time.|