Your hitting big jumps but you don't know how to carve on a snowboard? I'm no instructor so I'll let Snowwolf chime in, but one of the big things about landings jumps is where you are actually landing on the knuckle, (end ramp of the jump). You want to try and hit it at the right speed and pop so that you land where the ramp has the biggest pitch downward.
Because the knuckle is aimed downwards, what it does is it keeps your body's velocity continuing in that same direction rather then stopping it, which causes serious impact on the body. If your landing at the top of the knuckle where it's somewhat flat or past the ramp where it flattens out, that is when your going to feel the most impact because your body is just slamming on a flat surface rather then hitting the ground and then speeding away.
I really haven't done that many jumps, but the times I have I noticed this was a huge factor. The times I got the landing in the right zone it felt like butter, and then the time when I got WAY too much air off a small jump and completely cleared the knuckle and landed on the flat ended in me washing out because it was too much impact and slamming my hip.
You're using the term "knuckle" wrong. The knuckle is the part that transitions from the top of the jump to the landing. Like how the knuckle on your hand is the transition from one bone to the next. Hitting the knuckle in any way is bad and you always want to try and completely clear the knuckle. On most jumps landing just past the knuckle will give the smoothest landing. Be sure to watch out for the second knuckle created by people landing short and stomping out a new shape to the jump.
I can carve but I've got no help with how to do it.