Dotted brushes; they're oh, so simple... really.
Click on your Brush Tool 
so that it's active.
You need to choose an appropriate brush.
For this example, I'm using Hard round, size: 1 pixel.
Next, toggle your Brushes Palette.
It's location varies from each version of Photoshop.
If you can't find it, use the shortcut [ F5 ] and the palette should magically appear.
Once you're opened up the palette, click on Brush Tip Shape.
A new menu should appear within the palette now, with selections for adjustments of your brush.
Towards the bottom of the palette, the option of Spacing should be selected.
Below that, should be a basic preview of your current brush.
Adjust the current percentage of spacing between your brush to your own personal preference.
For this example, 400% is used as the spacing.
And that's basically it; you're done.
You can now expand your creativity by drawing with the Dotted Brush.