size of square, in pixels per side. It is not recommended that you set this much past a couple of hundred, unless you don't mind waiting a while.
"xsize" x-size of display
"ysize" y-size of display

"scale" scale of fractal, in percent.

Origin: ( , ) This is what point on the complex plane will be in the centre of the image. So for instance, setting this to (-1, 1) will put the centre of the actual image (the origin) near the bottom right of the image. Chances are you don't want these higher than 1 or lower than -1.
Iterations. This will create more precise images, but past about 100 there isn't really much noticeable change for most fractals. This severely affects the load time, so do not set it too high or you will never get your image :o)
+ i This is the value of c in the function z -> z²+c, the "Julia Set constant"
Red: Green: Blue: You can customize the way colour is rendered here by setting a multiple for each colour.
Brightness multiplier -- sort of the equivalent of adjusting all three colours at the same time

Try entering values of c close to the boundary of the Mandelbrot set. For instance:
c = i or c = 0.123+0.745i