WLet's start.
Fiscal and monetary policy are Macroeconomics instruments used to regulate the economy. Fiscal policies are regulated by the government. How? Through government expenditure and collection of tax revenue. The government can use it to address issues such as public debt. It is used to ignite economic activity, total spending, it's composition and aggregate demand. At the other side, monetary policy is used by central bank to control money supply, interest rates and credit in the economy. The IS-LM which stands for Investment saving liquidity money supply. Putting the two together, it analyzes the goods market and money market to determine equilibrium levels of interest rates, output and given prices. The money market creates the LM curve while the IS related to level of real GDP and real interest rates.