A stop-limit order is an order that goes live at your predetermined stop price and will be filled at your predetermined limit price or better. A stop-limit order does not guarantee execution if the market price does not reach the stop price during a specific time period.

Assume the current market price of a stock is USD100:

BUY: If you submit a buy stop-limit order with the stop price at USD110 and limit price at USD120, and later the market price rises to USD110, the buy limit order will be triggered. As long as the order can be filled under USD120, which is the limit price, the trade will be filled.

SELL: If you submit a sell stop-limit order with the stop price at USD90 and limit price at USD80, and later the market price drops to USD90, the sell limit order will be triggered. As long as the order can be filled above USD80, which is the limit price, the trade will be filled.