Stock market futures
If you have at least a basic knowledge of how the stock market works stock market futures should not be too hard to understand.
The stock market is open Monday through Friday 930-400. Any trading done after 400 is called after hours trading, any trading done before 930 is called futures trading. Futures trading is very important because it sets the tune for the entire day. The stock market does not just randomly open at one time, stocks are still traded throughout the day.
Futures trading is often dominated by how the Asian markets are doing. Asia is anywhere between 6-10 hours ahead of us so by the time most wake up the Asian stock markets have almost concluded their trading day. Economies are moving away from what is going on locally and focusing more on what is going on globally. The United States imports tons of things from Asia [literally] and we do a lot of trading with Asia so what is going on with China and India and Japan is very important to us. Also China and Japan hold a lot of our debt.
The average investor does not need to worry about futures trading. Just worry about the long term and make sure you are in a position to benefit from the markets returns in 5, 20, and 50 years.