The Fed's job is:

> The Federal Reserve works to promote a strong U.S. economy. Specifically, the Congress has assigned the Fed to conduct the nation’s monetary policy to support the goals of maximum employment, stable prices, and moderate long-term interest rates. When prices are stable, long-term interest rates remain at moderate levels, so the goals of price stability and moderate long-term interest rates go together. As a result, the goals of maximum employment and stable prices are often referred to as the Fed’s “dual mandate.”

* https://www.federalreserve.gov/faqs/what-economic-goals-does...

There is a tension between maximum employment and stable prices though: if the economy is starting to run hot, it means more and more people may be employed to keep up with demand. But if there's too much demand, and not enough supply, inflation starts kicking in (there are other sources of inflation though). So the 'trick' is to know when employment has reached the point of being 'maximum enough', and slowing down the economy then.