Ok this tutorial assumes the following things a)You can read b)You can follow simple instructions c)you have gimp d)(Optional)You have half a brain.
Ok First make a new image! Make it HUGE (You can always make somethig big smaller, but making something small bigger will give quite a big quality loss) Second make a background colour! (Black is prefered) (Optional) Set foreground and background colours! Go too filters>render>Flame Change the settings so it covers the whole image, or the area you want it too cover. Click 'edit' play around till you find something you like (optional) Play around with colours>Hue saturation untill you are happy
Save it as a nice format (Preferably PNG)
Congratulations! You have made some nice abstract art!