Complex sentence: River was born and raised in Mississauga, a city within the Greater Toronto Area; he attended Clarkson Secondary School, where he began writing songs and participating in rap battles that took place in the school's stairwells.
Split into simpler sentences: River was born and raised in Mississauga, a city within the Greater Toronto Area. He attended Clarkson Secondary School, where he began writing songs and participating in rap battles that took place in the school's stairwells.