Still not understanding radial w/ transparency gradient

Question

I am trying to create the effect of a soft glow light behind a subject.
I must be going dumb, but part of the problem is simply not "getting" the zen of doing gradients in PE, partly because everyone's very helpful suggestions seem to vary so widely on how to do it and I'm getting more confused.
What I want to do is have one color (say dark red) where I can control its saturation, size, etc. and have everything else be transparent. I will be putting this graphic later on a website that has a colored background so I need the effect of the light being cast on that background.
The more I try to learn gradients, the farther way the knowledge seems to be.
Can anyone walk me through this?
Thanks. 

Answer 1

Tip: "delete" refers to hitting delete on the keyboard.
http://www.pixentral.com/show.php?picture=1HpboRcB57ewPTvyui1MUeb9mI4WBR0
This is as close as I can come to your request:
Select background color 0,0,155 (can be any color, but this shows up well)
File>new>blank file, 400px wide, 400px high, color mode RGB, resolution 300px/in
Access Custom shape tool. In options bar set color to white, and in shape library for this tool select the triangle shape. Click on the little triangle at the top to get the shape geometry options. Select fixed size. Enter 260 px width, 225 px height. Click on canvas to create triangle.
Now choose the oval shape in the library. Change geometry to 260 px wide, 50 px high. Click on canvas to create oval.
Access move tool, and nudge oval into position at bottom of triangle with arrow keys  In layers palette, link the 2 shape layers and merge them (Layer>merge linked)
Select foreground color red
Select gradient tool, in options bar select foreground to transparent, linear gradient
In layers palette, CTRL+left click the cone layer thumbnail to select it - should see marching ants
Drag from south to north within the selection to to apply the gradient
Select>deselect
Here is a print screen to demonstrate the layer structure:
http://www.pixentral.com/show.php?picture=10Hst6bjMVa0qFttqIBp9CI6ry5id
Note the linked layers referred to above - #5
If you finally need to delete the blue background for your purpose, you can do this readily utilizing the magic wand tool.
HTH