Okay so what you will need is a camera that can shoot a continuous burst rate of 7+ for starting. Take a good tripod and set up your camera by the feature you are taking the photos of. I would recommend shooting in manual so that you don't have any light or color variation. Then you will want to take a photo without the subject in it. This will be your base photo. Make sure your camera is in continuous shooting mode. Then when you are ready have the skier go and make sure to start shooting right before they hit the jump so you don't miss it. Let go of the shutter when the skier has reached the point you desire.
Editing- Go into Photoshop or a similar program, a free alternative is
https://pixlr.com/editor/. You will have to import your first photo, then make it your background. Then add your second photo over it by clicking Layer_Add image as layer. Then you will have to select the eraser tool and erase the part of the image where the skier was last. Continue to add layered images and erasing until you have your result! Hope this helps!