You may see a warning like this the first time you add the token, this is normal:
Connect your wallet to the exchange using the "connect to a wallet" button in the top right corner.
Change the slippage to be above 5% (6% is recommended), this allows for the 5% R3FI fee:
Enter the amount of R3FI you would like to buy and follow the steps there. You may need to enter a round number such as 1000 instead of 1000.123 for transactions to work.
All done! You now hold R3FI and your wallet will begin earning yield rewards from transactions without any further steps.