I am trying to green screen a video in blender, however when opening the node editor and clicking add I cannot select any nodes and cannot see the node I am looking for. I have the following menus: Add, Search, Input>, Output>, Color>, Vector>, Converter>, Group>, Layout>. Is there something that I was supposed to do before adding the node other than importing my video files? Any help is appreciated, thanks 
EDIT: That worked thanks Richard. Although I still cant select the node I want to use. Its dimmed out. Is there something that I need to do before adding the node?
EDIT2: Found it… clicked “use nodes”