A stop loss is an order that you give your broker to "stop losses" ("stop loss").
The golden rule of stock market speculation is to always keep risk under control. To do this, you have to know how much you are willing to lose before buying your shares.
Once you know or decide that figure, you will give an order to your broker to open the position.
In addition, immediately after giving the buy order, you must also leave a stop loss, which is a sell order that will only be executed if the price falls enough to cause you your maximum allowable loss. In which case, your shares will be sold before suffering greater evils.
You should know that the orders that are not executed are free; so controlling the risk in your stock operations will not cost you anything, but it will save you a lot of trouble.
Trading the Stock Market without a stop loss is like driving a car without brakes. Always use a stop loss.