Ramesh:
Screen #1 shows the P3 interface. It's used with the most advanced workbenches in CATIA. (I've never used it and never saw anyone else use it either)
Screen #2 shows the P2 interface. This is the interface that most CATIA users use.
There is also a P1 interface for the entry-level of CATIA. (I've never used it, but I think it has the same screen layout as P2)
You can choose which CATIA interface to use in the Tools + Options + General section. Or you can go to Start + Programs + CATIA + Tools + Settings Management and choose a interface there.