The fiscal policy and monetary policy are both used to support economic growth. However, the key difference between these policies is the attributes they manipulate.
The fiscal policy is the responsibility of the government and changes the levels of taxation as well as the amount of government spending. For example, if the government wanted o increase economic growth and demand, it may look to reduce taxation and increase its spending.
The monetary policy is the responsibility of the central bank and sets changes on base interest rates and supply of money (for example policies on quantitative easing to increase supply of money in an economy). For example, if an economy went into recession, the central bank would likely cut interest rates in order to encourage spending rather than saving in an economy.