How is it possible?

There are brokerage companies that enable you to buy and sell different currencies through the Internet and some simple softwares. For any trade that you make, you pay a small commission to the brokerage company that you are trading through it.

You need to find a good, reliable and well-known brokerage company and sign up for an account with it. Then you have to fund your account. You use the money you have in your account to trade. Any profit that you make, will be added to your account and visa versa. Then you can withdraw the money you have made.