First of all, the rumble occurs because of an ongoing turf war between the Greasers and the Socs. Ponyboy and Johnny do not want to fight, but they get caught in the park.
A rumble, when it's called, is usually born of a grudge fight, and the opponents just happen to bring their friends along. (ch 1)
Ponyboy gets in a fight with Darry and runs away with Johnny, but Ponyboy and Johnny get caught in a rumble in the park in which Johnny accidentally kills a boy. Johnny and Ponyboy go to Dally for help. He then instructs them to find an “old abandoned church and “[buy] a week's supply of food.”
“[This] morning, before the story gets out, and then don't so much as stick your noses out the door. I'll be up there as soon as I think it's clear.” Ch 4)
They do go to the church, and everything is going fine until a fire starts and the boys try to rescue some kids who are on a field trip. Johnny gets hurt, but before he dies he has advice for Ponyboy.
"Stay gold, Ponyboy. Stay gold..." The pillow seemed to sink a little, and Johnny died. (ch 9)
Johnny is referring to a poem the boys discuss called “Nothing Gold Can Stay.” He is reminding Ponyboy to stay good and pure, and be the good person he knows he is despite what they have gotten mixed up in.
The Socs backed off of the Greasers