A beginner question, I am puzzled about futures on the S&P500. I believe the futures contract arranges a price to purchase the underlying at fixed dates in the future (such as expiring in March); most often this date is not tomorrow, and is often weeks away.
However, people seem to talk about the overnight value of the future as something
that might relate to tomorrow's price, for example in this question
how to use the sp500 future to predict the stock market
If the contract is for a month in the future, why would it have much to do with the price tomorrow morning?
For example, if the S&P is at 3500, and I am selling a contract for 6 months (or even 1 month) in the future, I may believe the index will rise by 5%, and thus should be unwilling to sell a contract for near the price that it will be tomorrow.