Stop loss is use to minimize the loss you could suffer just in case the market went to the opposite direction of your trade, because it will stop your trade once it’s triggered on a certain price you’ve set it.

If I’m not mistaken, it’s always visible on the trading panel in futures, you just have to explore UI of whenever platform you’re using in trading. If you can’t still see it, for sure there’s a lot of YouTube tutorials regarding about the exchange where you’re doing your trades.

Using stoploss depends on you risk to reward ratio.
If you have a risk to reward ratio of 1:3, then you need to place your stoploss at a distance that corresponds to one-third of the potential profit target,
this will be profitable because your risk exposure is limited while allowing the trade sufficient room for price fluctuations within that established risk parameters.

Maybe at least tell us what platform so we can help you? Because It’ll totally depend on the exchange you’re using. And chances are, whatever platform you’re using has an article on how to use their stop-loss function so you’re better off Google-ing it first.