There's a brokerage company that lets you buy and sell various currencies over the Internet and some simple software.
For whatever trade you make, you pay a small commission to the brokerage firm you sell.
You need to find a good, reliable and reputable brokerage firm and sign up for an account with it.
Then you have to fund your account. You use the money you have in your account for trading. Any profit you make,
will be added to your account and vice versa. Then you can withdraw the money you have earned.