Let's look at the Toolbox once again. As you can see it is full of some (supposedly useful) instruments. Let's try some of them.
§ 1. Open an image file [Ctrl+O] from our sample folder.
§ 2. From the Toolbox, select the Brush Tool.
§ 3. In the Options bar, define brush tip size as it is shown in the movie.
§ 4. In the Swatches palette, click a color you want to paint with.
§ 5. Paint over your image.
§ 6. Open the Brush Preset picker and harden your brush - for sharp-edged strokes - or soften it for gradual color transitions.
§ 7. There are some more controls for the Brush Tool in the Options bar. For example, you can reduce the "Opacity" value. Now the Brush paints with transparent strokes allowing seeing the previous content.
Tip. Just in case you didn't know, the Brush tool is also available in Photoshop Elements that is way cheaper version. And if you believe, Photoshop Elements lacks some other important feature, be sure to visit this page.