Contestants are partnered up to perform a particular style of dance each week. Starting with 20 dancers, viewers vote each week on their favorite couple, leaving the bottom three couples with the lowest number of votes up for elimination. After each dancer performs a solo of their choice, called "Dancing for their lives", one male and one female contestant are eliminated by the judges.
Once the dancers are whittled down to the top 10, the couples continue to dance together but viewers then vote on their favorite dancer rather than pair.
If I had a complaint - it was watching that Bieber person with his choreographer (who was himself a smarmy character). The whole 'dance crew' was pointless and felt like the outcome had been jury rigged.
But otherwise a tremendous show filled with amazing performances of world-class choreography.