Tip: use the "add" layer blend mode Tito get the fire/ flame effect.
Follow below steps:
1. Use the flame brush and make Radom scattered strokes with orange color
2. Then lock the transperancy of the layer and paint some random strokes of red color. ( since the transperancy - pixels - are locked, red only happens on top of orange color)
3. Duplicate the layer
4. Change the background to black.
5. Most important: now change the top layer mode to "add". You see the magic :-)
6. Using airbrush paint some glow affect in a bottom layer.
7. You are done!