It's the economy, stupid!

The experts are all over the map when it comes to the economy of the US and the world. Some so-called experts are even spewing gloom and doom, while others say our economy will grow from 5 to 7%.
China devalued their currency, and all of a sudden, the world economy is going to collapse.
I understand that all economies are tied together as never before, but why would China's devaluation of their currency affect the world's economy?
Can somebody please explain the macroeconomic impact of China's currency devaluation?
The unemployment rate in the US is at its lowest in many decades. I think the last number I saw on adding workers was 230,000. I see this as more income and more spending resulting in more demand for goods and services.
What am I missing?