Question about After Hours Voodoo

[Nanomite]

So I work late, get home and see if or what the market did today and I think it's a good time to buy. So being the total freaking n00b that I am, I'm looking at a S&P index fund SPY. I buy a 100 shares at 93 (after hours) at a limit order... First mistake and I understand why. It opened at 96 and the order was canceled.

What I'm trying to understand is how or who decides what a generic index fund opens at while in pause mode overnight?

I understand limit orders can be deceased and the market moves in steps, not curves. But where do these futures (steps) come from?

[srm555]

The S&P index is composed of 500 stocks and the value of the SPY exchange traded fund follows these pretty close. If there are more buy orders on these stocks in the morning, the price of the stocks will rise until they meet a balance price of those willing to sell. The SPY is just the ETF following the prices of all these stocks. The futures will give you a rough idea of where the market will open.
Not sure I understsand your second question.

[Nanomite]

Thanks!

The second question is who keeps track of the balance price of those willing to sell?

In other words, where are the futures derived from?

[Horsefish]

What I'm trying to understand is how or who decides what a generic index fund opens at while in pause mode overnight?

Those stocks in the SP500 trade overnight in the Asian markets and then the European markets. If you look at a streaming quotes screen after 8:15 AM and before 9:15 AM eastern time, you will get an idea of where a stock or ETF will open at.