I have been having problems with composite nodes on single layers. I add a viewer node and select the layer I want on the render layer node but the effect is still applied to the the whole scene how can I fix this?
maybe a window dump of your screen would help sort this out? where in your node setup does the effect come that is at issue?
I don’t understand any of that
Show us your Node screen setup by using the PrintScreen key on your keyboard (which copys the active screen to the clipboard in memory) then paste it (CTRL-V) into your favourite paint program. Then save as a jpeg and upload it here.
I’m doing this on a Macbook so I don’t have a print button
I took a screenshot of blender but now I can’t put it this the website, maybe I just need a good tutorial.
make sure the camera is a member of all layers.
That is it!, I hope
wait, no only the layer that uses nodes shows up 
Well I got the two together but it’s only the alpha values
if you were wondering, I have been using the tutorials on this webpage I just finished the 3rd tutorial
http://www.animationforcreation.com/2009/06/make-fire-in-blender-3d.html