Hi Senthil

It might help if you could give a few more details as to what you want to achieve. At a basic level the following command will turn on RSTP on a 6500 IOS switch

6500(config)# spanning-tree mode rapid-pvst

And then you can manipulate port costings by going into interface config mode

6500(config-if)# spanning-tree port-priority "number in increments of 16"

But there is a lot more you can setup with STP/RSTP and it all depends on what you are trying to achieve.

Jon