[1] Call options[2] give you the right, but not obligation, to sell an asset at a given price, so if the strike price of the option is the price you don't want the BTC to go below, and the price of BTC does go below that value, you eliminate your downside risk because somebody has already agreeed with you to buy at that price - and you have to pay for that agreement up front.
[2] Options ~= Insurance, where ~= means 'pretty much equals'