How do I buy stocks at the market open

Hi,

I’d like to buy stocks at the market open. I want to place the order the night or day before. How do I do that?

I tried it last night by putting in a market order, but I didn’t get filled at 8:30 am CST.

Also, how do I attach a stop for a position? I tried that I got filled immediately.

Please advise.

US stock market is closed today January 20