Options question.

Before, I didn't even try to get into the essence, but lately many friends are addicted to options, and I also wanted to figure it out. If someone can explain it on the fingers, буду признателен :)
The first question – technical nature. Suppose, I bought option way to get Sbera at the price 8500, the underlying asset has fallen in value, option price, respectively, Grew, I decided to sell the purchased option – Do the risks pass to me as a seller or not? Or it is considered, that I am closing the position. What will happen, if i decide to exercise the option?
And another example. If I buy a put at the price of the underlying asset 8500, with a strike 9000, if the price goes above the strike, option value is zeroed? It makes sense to keep it, if suddenly the price goes lower, or all?
Or if the strike, say 7500, and the price went below this mark, does this mean a good bonus?
What's better, in this case, (if the price goes down in the future), buy with a strike 9000 or 7500?