Unlike forex and cryptocurrency, where the number of buyers and sellers determine prices, index prices move based on the price movement of equities that are represented in it. These companies could be from one particular sector, like the Nasdaq 100, which represents technology companies, or the DAX 30, which tracks the top 30 companies on the German stock exchange.
Big changes in equity performance in a particular sector can impact index prices, especially if that sector occupies a large portion in the index. Also, it is important to consider market correlations. For instance, forex market movements can impact the domestic stock markets, and subsequently an index.
So, it is important to keep track of economic data and news releases that cause intense buying or selling pressure in the chosen index. For instance, the US Non-Farm Payroll report and US Federal Reserve announcements can cause major volatility in many US indices, including the S&P 500, DJIA and Nasdaq 100. The Euro Area GDP figures and inflation data can impact the DAX 30 and Euro Stoxx 600.