To do a ski jump you basically wanna think of it like a squat jump but the focus is on moving your body not just up and down but moving side to side. It's a lateral exercise. So you get into a position like your literally going down the slopes, into that skiers stance, so your knees are flexed, your chest is up and your gonna jump up and to the side, just making sure that you take off from both feet, and you land on both feet as opposed to kinda coming down and off of one leg at a time. Again, both feet up, both feet down, sinking back onto your heels so that most of the weight is on the back part of your foot. You can progress the ski jump, by doing it up and over a bench or a box. The higher the box, the wider the box the harder its gonna be, but the same rules apply. Watching that your knees don't go in, don't go out and you maintain the integrity of the squat position and then traveling up and over, latterly moving that squat from right to left. Once you get stronger at the ski jump you can play with how you do the exercise, maybe you wanna go for a little bit more speed, a little bit more height, or a combination of the two and make it more of a power move. Lots of different variables that you can use, but the important thing is, is that you got strong landing mechanics, decelerating and working through your muscles, keeping your core engaged and breathing.