Assume you want to trade a gold binary options contract, because you believe the price of gold will rise today. You can buy the option at 50. If you are right, and gold is higher than the strike price (price level of gold that determines if you are right or wrong) when the option expires, the option will be valued at 100. You make a $50 profit on each contract you buy. If gold is below the strike price when the option expires, its value is 0, and you lose $50 on each contract. 
For US residents, Nadex is by far the best trading service available. Unlike other offshore brokers, Nadex offers trading via an exchange and is the only broker that is licensed in the United States. Apart from its activities being monitored, being licensed ensures that traders will always have legal recourse in case anything goes wrong. And by offering binary options trading through an exchange, Nadex allows traders to trade against each other; there must be a seller for every buyer. This way, there is absolutely no vested interest (on the part of the broker) and traders do not have to worry that the broker is on the other side of their trade.
The FBI estimates that the scammers steal $10 billion annually worldwide.[11] The use of the names of famous and respectable people such as Richard Branson to encourage people to buy fake "investments" is frequent and increasing.[12] Articles published in the Times of Israel newspaper explain the fraud in detail, using the experience of former insiders such as a job-seeker recruited by a fake binary options broker, who was told to "leave [his] conscience at the door".[13][14] Following an investigation by the Times of Israel, Israel's cabinet approved a ban on sale of binary options in June 2017,[15] and a law banning the products was approved by the Knesset in October 2017.[16][17]