Fill in the background with what ever color you want your frame to be using the Fill tool.
Next, create a new channel and create your shape using the Rectangular tool, (you may choose to use
the Ellipse or Polygon). The shape you create should be filled in white. Hold down the shift
key to keep the shape as a perfect square or perfect circle.
Now it is time to add the style to our frame.
Filter -> Blur -> Gaussian Blur (I use 4px here).
Filter -> Pixelate -> Color Halftone... (I keep everything at the default settings).