It's alright. I've figured it out. Indeed, you do need the node compositor.

I'm using the Blender Renderer. You need to tick nodes, and change the node editor mode to Compositor.

You have your input nodes and then your processing nodes. If you want to see the changes before render, you link the output to Viewer node. If you want your result to go to render, that is enabled by (even simultaneously) sending the post-process output to a composite node.

Thanks for all the effort.

By the way, you insert from a node by hovering the mouse cursor over the transitional ({operative) processing value, and use the key for insert to the dope sheet or timeline. It's all in the key, and where you hover the mouse! Sheesh!