The following tutorials were found by Googling “green screen [name of program] tutorial”. If you find other tutorials that you think would be useful to add, please email me a link to them.
Thank you William for suggesting this one:
Before working on green screen, you will want to watch this video on how to add your video to a new Premiere project. Here are two that might help.
Notice that the green screen video is the top layer with the backgrounds underneath it.
Notice that when he rearranges the order of videos, he pulls it down by grabbing the name of the video.