is there any command in ug nx similar to fill command in catia
It's been almost a year since I've used NX, so I apologize if I'm rusty.
I'm assuming you're asking how to convert a body made out of many sheet bodies into 1 piece of solid geometry. After you create all your surfaces, you can use the Sew tool (should be Insert->Combine->Sew). Select all the faces that bound the body, and as long as it is closed, it should make a solid.