All you'll need for this tutorial is an image and a desired colour scheme.
Start by opening your desired image. Then create a New Layer above it.
Select the Brush tool and using the default brushes at the top - match your setting's to the one's below.
Select your desired Foreground Colour and click the image as many times as you like. Add as many or as little orbs as you like.
Change your Orb Layer's setting's from Normal to Screen. If it seems to bright, you can always lower the Opacity a bit too.
If you wish to add a pattern on your orbs, then double click the orb layer. A blending options box should appear. Go to Pattern Overlay, select your desired pattern and
settings. Once you're happy, press OK to save the changes.