I've asked this before but I lost the email telling me what to do. I have a vid of me jumping, but I want it to appear like I'm jumping way farther than I am, so what I did was cut the video right at the top of my jump, record empty backround, then filmed myself landing far away. I then took a still picture of myself and I want to use that to fill in the middle of my long jump. I masked out my body in the still picture but I don't know how to place the mask of my body onto the empty backround! I tried to copy and paste the mask onto the backround footage, but it only showed the yellow outline of the mask, not what was inside.
Here's a tutorial that shows how to do what you're trying to do:
I think that you're misunderstanding how masks work. To overlay an image of yourself onto a background, you need to place the layer that includes the image of yourself over the layer that contains the background. The mask's role is to determine which part of the layer is visible and which part is transparent/invisible.
I recommend that you work your way through the materials here: