Benvilo and Romeo were just walking around the area and talking to each other before Tybalt enters and starts to make a mess
Tybalt chaallenges him in a battle and asks to fight him.
Mercutio comes in and protects Romeo. He tells Tybalt to fight him instead of Romeo and the fight begins.
As the fight progress Tybalt eventually stabs his sword into Mercutio's stomach. Mercutio tries his very best to stay alive and keep fighting but eventually fails and dies.
Romeo rage and anger gets so extreme that he challenges to fight Tybalt because he had killed his best friend,Mercutio. The fight s intense and Romeo's anger and hatred reaches a peek.
As said in the previous scene Romeo anger got so high the he eventually stabbed Tybalt which leads to Tybalt becoming dead which is not good because Tybalt is the princes cousin and related to the Capulets and wants to make peace with them for his relationship with Juliet to be sucsessful.