In the last week or so, I've been learning photoshop. Between all the tutorials on DeviantART and guide on the web.

1. You can get free brushes online.
- Brush King [link]
- Free Photoshop Brushes [link]
- Brusheezy [link]

2. The difference between Opacity and Flow:
Photoshop brushes work by placing down discs of color (or shapes) as you move the brush around, one after the other.
-Opacity is how much 'color' is placed down.
-Flow is how often a circle is placed.

3. Glow Effect
I honestly found the easiest was to use very low opacity and use white and whatever color you want the glow to be of. Then clicking a lot at verious sizes.
-There is also an inner and outer glow effect in the settings by double clicking on the thumbnail.
-Using a starburst shaped large brush at low opacity in white helps too!

4. A wonderful wonderful painting guide by Sandara: [link]