Basically you set a "trigger" price and a buy/sell price, whereas your buy/sell offer will be listed if that certain trigger price is reached. Stop limits are used just as a sort of safety net just to somewhat hopefully minimize your losses when a certain coin's price crashes.
Hopefully you can understand it better by looking at the screenshot below (from Bittrex). Look at the conditional options.
I dont understand too how it works but this post made me realize how the stop limit works, thank you mate.
I will try this later, and seems like i can go outside using this.