Economic policy is the instrument available to the government to change an economic reality, turning it into something better or worse. That is, government actions through economic policies are the cause of good or bad effects on the economy.
For example, the stimulus to unbridled credit, as in the 1920s generated a super production that found no consumer market, which led to a huge economic crisis and culminated in the depression of the 1930s.
Another example, if a government injects a lot of money into an economy, it will cause inflation. The cause is the expansionary monetary policy (a lot of currency) and the effect: inflation. The cause-and-effect relationship is direct.