Lyne, I don't think anyone answered yet what a Render Node is.

 

This is so you can build a 'render farm' of more than one computer.  So if you have another computer that you want to help you render something, you put the Render Node on the other computer, make sure the 2 computers are communicating able to see each other on the network, and then you can set it up to network render with 2 computers (or 3 or 4 our however many extra computers you have hanging around) instead of just relying on you main computer.

 

For example, my main laptop is an i7, so it renders with 8 cores.  But I have an older backup laptop that runs with an i5, which renders with 4 cores.  So if I set them up on a batch render to render together, that means I have 12 cores rendering at once (the cores from the render node aren't colored, they are all gray, but who cares, it's 4 extra cores cutting the render time).

 

I set this up to test it when I got my new laptop, haven't used it since but it worked fine.