How LSD and Positraction works??

I'm kinda confused on how a limited slip diffrential and Positraction works. I know it deals with traction (duh!) of the drive tires and I know that you cant get good launches in high HP applicatios without it. Could someone explain?

A limited slip differential is a differential which directs torque from the driveshaft to the wheel that isn't slipping, basically.

Positraction was just a name GM used a long time ago.