The "Twinpower" turbo is quite straight forward.
Generally in a twin turbo you would have both a low pressure and high pressure turbo. High pressure turbos give you the push you're looking for, but but they result in "turbo lag" (you hit the pedal and it takes a second or two to spin up and start shoving the air through. A low pressure turbo provides a fill in for the lag, so you hit the gas, the low pressure turbo kicks in, starts ramping the fuel/air mixture into the chamber, then the high pressure turbo catches up and takes over - no (or little) turbo lag.
The twin scroll turbo design starts off as a low pressure turbo, then the fans rotate to basically become a high pressure turbo. So, you get both turbos but in one housing.
At least that's my understanding of how it works.