The video tutorial begins at 0:50, so you can skip to that.

1. Stand the green screen vertically, as shown in the video.
    
2. Put one hand on top and the other on the side.
    
3. Using the hand that is on the top, twist your arm away from you body, whilst pushing the green screen down.
    
4. Tuck the top of the green screen into the middle.
    
5. You should be done. Make sure to watch the video for visual cues.