Bhairava,
How do slide the rear tire? Easy, you apply the throttle coming off the corner until the rear tire starts to spin. Once the tire starts to spin you slowly roll off the throttle. Garry McCoy is VERY skilled at modulating the throttle to make the long slides that you see him make when he exits corners. It takes lots of practice.
The rear brake is usually not used to make the rear slide, unless the rider is using it coming INTO the corner. This is sometimes what causes the rear tire to slide around when guys are "backing it in" to a corner.
When you do Level 4 at the Superbike School you get to ride our Slide Bike where you will learn how to deal with rear wheel slides. It is a lot of fun too!
Timmer