If any one knows about power switch please help me.... How we insert them in the design and How they work ..
If any one has good tutorial on that or any pdf link please help.
A power switch gates a power or ground rail with an enable. It is used to turn-off power to gates (e.g. a block) for power savings. Typically power gates are inserted in P&R.
There is a comprehesive tutorial here:
Power switches are now very common so I imagine there are many other tutorials online. Google search "low power switch".