If America dies China will be the next superpower. How is this possible?

[Harold]

O*no racism is intended in this question and I do not with to start a flame war*
China's economy is the strongest next to America. How is this so and how does this economy thing work?

I don't even think they are a developed country, their infrastructure is bad(looks like buildings from 50 years ago), their poverty rate is high, there are still many villages and people who live in the mountains that has never seen the city, super high corruption rate and many more. Basically they look nothing like a developed country if you go for a walk down the street. The country as a whole/most of China) is dirty like they don't have a road sweeper and their citizens doesn't give a f**k.
The only thing I see they have is a sh*t load of fuel and manpower. Their currency is lowTheir tourism rate is low.
Can someone explain to me how this economy thing works?