Explosion on paint.net. If you done it right, it should look like something like the image.
Step 1: 1: the "Main Part of the Explosion".
1. Make a new picture, 800x600
2. Go to Effects>Render>Clouds. Click OK when a window pops up showing properties for the 'cloud' thing.
3. Duplicate Layer. (Shown on picture below)
4.Go to top layer, then Effects>Distort>Bulge. Make the value 100.
5.Go to bottom layer, then ffects>Distort>Buldge. Make the value -200.
6.Go to the top layer, then go to Properties (on picture below), then change the blend form to "XoR".
7. Flatten the layers. (Below)
Step 1: Done, should look like image below.
Step 2: 2: Step 1: Continued...
8. Duplicate the layer (Shown on last step's picture... =P)
9. Effects>Blur>Zoom Blur. Change the value to 75. (Should look like picture below.)
10. Go to top layer, then Properties, change blending mode to "Lighten".
Step 1 is done!
Step 3: 3: Step 2!
NOTE: The last 2 step make up the main part of the explosion. These steps will show you how to color it.
11.Adjustments>Curves. Change the type to RBG(Red Blue Green), and
then look at the image to find out where to put the markers.(First, start with Red. When your done with Red, uncheck it, and then check Green. Do the same thing with Blue.)
Step 4: Instructable: Done...
This is my FIRST instructable, so dont be harsh.
PS: You could do a little "playing" with the 1st step's result to get very cool images.
Here's some on the bottom...
1. Some flaming ball
2. Sky blue ball with Yellow/White/Blue/White Lining
3. Green like explosion with yellow in it
4. Orange and yellow colored ball