Complex sentence: In the next phase, the Top 100 contestants are randomly put into groups of four and the groups choose a song from a short list of pop songs and they are given all night to rehearse so they are able to perform it next morning.
Split into simpler sentences: In the next phase, the Top 100 contestants were randomly put into groups of four and the groups chose a song from a short list of pop songs. They were given all night to rehearse so they would be able to perform it next morning.