Okay - nodes can be confusing - serial, parallel, outside and so on. I'll be taking a look at those in due course, next week we finish off on our tour around the Color window (making some adjustments as we go), then the following week I'm hoping to start colour correction and grading (and that means adding nodes).
It may help to think of serial nodes as layers, as you would find in other photo / video editing packages, so you might want to do your basic colour corrections in Node 1, then apply some grading in a new serial node (Node 2), then add another serial node (Node 3) and an outside node (Node 4).
Select Node 3, add in a power window to select part of the image and make your adjustments - they will only affect what's inside the power window.
Now go to Node 4 and make some more changes... Node 4 is an outside node, so it will only affect anything outside of the power window you set in Node 3.
Does that help a little bit?
Parallel nodes are also really useful, and I sometimes use them for dealing with skies - but more on that later
