has a “Sign Up” button in its top-right corner. Click it and you'll see this page: 

Once you've made an account and signed in, you can add or remove token funds from the exchange. Hover over "Funds" and click "Master Account" to transfer funds to your account.

Once you have funds in your account, head to the Token Trading page to buy $RFR. Hover over the Pair Markets image in the top-left to expand a dropdown box that allows you to search for RFR in the exchange.

You can pair $RFR with whichever currency you wish to transact with, including US dollars. Enter the amount of $RFR you want to buy, then click the green Buy button near the bottom of the page. Congratulations, you just bought $RFR!