You will set a two prices here, if the price you set in stop price will reach the current price, it will open another order with price you set in stop limit.
Example: You set stop limit with price at 12,000 and limit at 11,900.
This mean, if the price will reach at 12,000 it will open an order with the price of 11,900.
It's two prices because it is Stop limit, not stop market.
In stop limit, you will set two prices, the stop price and the stop limit.
Using the stop market, you will only set 1 price here, where if the price you set will reach the current price, it will create an order based on the current price, it may not exactly not the same price you set.
So its a way of hedging your bets if the market starts to crash you can "Detect it" with your stop limit price, then you can dump all your BTC at a lower price. Why wouldnt you just sell at 12,000 and not 11,900?