/biz/ - Business & Finance

Explain this to me like I'm retarded

Yesterday, a certain stock was worth $17,70. I thought it'd fall to around $16,20, so I bought 600 put options at 0,75 each.
Today, the stock has plummeted. In the morning, while it was worth around $16,50, the options were worth $1,10. Now, the stock is worth $16,10 and the options are $1.
Why is it that the options' price fell? When buying them, should I aim for the lowest reasonable price possible? Why?

I tried reading investopedia, but I got lost between buying/selling calls and puts
I don't understand what values when and why.

friends, I'm dumb
how do put options work?
if ABCD4 is selling for 10$ and I buy a put option for it at 9, where do I profit?
if it falls for lower than 9, no one will buy it, right?
and if it goes for 9.5 or 10.5, i'll only lose money

can someone explain for the brainlet?