Texture Mask is an especially useful node as it gives you the flexibility to create custom soft-edge shapes for your Texture.
From the node of your desired texture, drag the Texture output pin and choose Texture Blend from the Search menu. As a second texture, select Texture Mask node.
Click Setup button to start.
In the Mask setup window you can add, rename or delete multiple polygons.
To add your first Polygon navigate to the Setup section on the right hand side of the window and click Add polygon.
To move a polygon, select the moving handle on the top left corner of the polygon shape and drag it to the wanted position.
Each polygon mask has it's unique properties. You can see what they are in the Edit and Texture sections which appear only after you have selected a polygon mask.
Our default polygon has a Linear transition but you can change it to Radial or Uniform in the Type dropdown menu.
You can customize the shape of a polygon by adding and removing points.
The first way to add a point is to double click on a spot you would like the point to be created. The second way to add a point is to right click somewhere on the canvas and select Add point here.
To remove a point, just hover over it right-click.