From Genius:

"Guns N' Roses introduces itself with a hard-hitting ode to a wild place that can tear anyone apart. No wonder it’s their usual setlist opener (except in the Chinese Democracy tour, where the eponymous song did the honors) and a mainstay of many sports events.

According to an interview published by Hit Parader in March 1988:

Axl wrote the words while visiting his long-time friend Tori in Kingston, Washington, a town outside of Seattle. It’s a big city, but at the same time, it’s still a small city compared to Los Angeles and the things that you’re gonna learn. It seemed a lot more rural up there. Axl just wrote how it looked to him. If someone comes to town and they want to find something, they can find whatever they want.

There has been said that Axl and a friend heard the exact same phrase that is used in the song from the lips of a homeless man, as soon as they climbed down from a bus, just after arriving in New York:

You know where you are?
You’re in the jungle, babe
You’re gonna die!"

Basically he is deriding the commodification of human activity and warning against the dehumanization and alienation that is caused by the habits of consumerism driven by capitalism.