Choose the Brush tool (B) and, in the Options Bar, pick a brush shape from the Brush Picker, then set the brush opacity. In this example, I used a 66-pixel brush called Dry Brush Tip Light Flow from the default set of brushes, but don’t forget you can always tweak your brush in the Brushes palette. Click on the Foreground color swatch at the bottom of the Toolbox, and from the resulting Color Picker, choose the color you want to use. I used black in this case.