I'm a pt and online coach and don't worry, people do struggle with a lot of core exercises so you're not the only one! To do a crunch, lay down with your back on the floor and your knees bent but with your feet on the floor if that makes sense! Put your hands on your quads and then as your back comes off the floor gradually move your hands up your quads towards your knees. Do not go any further than your knees. Then repeat 🙂