Go to File > New and create a new image with a white background.
Now go to Filter > Render > Clouds, then Filter > Render > Difference Clouds, and press Ctrl and hold down whilst you press F. Then repeat.
Go to Filter > Sketch > Halftone Pattern, and make sure 1, 5, and Dot are the options, then press Ok.
Press Ctrl and U and check the Colourise box. Then move the sliders around till you get the colour you want, press Ok and save. Alternatively see my colourising tutorial.