Upbit, an exchange hosted in South Korea, makes it easy to buy $RFR. These instructions will be for the translated English version of upbit.com

Click the "Sign up" button at the top right of their home page. 

You'll need to create a "Cacao" ("Kakao") account. Click "Login to cacao account"

Read their terms and conditions, and if you agree to them, continue to the next page.

Add your information and create an account. 

Once you're signed in, you can transfer funds on the Disbursement page, located in the top bar. You can use the green Deposit and Withdrawal links to connect your wallet addresses and transfer funds to the exchange.

Once you have funds, go to the ExchangeInvestment tab and use the search bar on the top-right to look for RFR.

Buying and selling is done in the middle of the page, near the bottom. Enter your order and click "Buying". Congratulations, you bought $RFR on Upbit!