Step 1 : Start with a new file 250x250, white bg. Set your fg and bg colours to default ( press D)
Step 2: Go to Filter>Render>Clouds
Step 3a : Now go to Filter > Distort > Polar Coordinates and select "polar to rectangular"
Step 3b : Now to add to the final fire furnace! - Press Ctrl + U to bring up the hue/saturation window, and click on a fiery colour of your choice!
More Tutorials: 
