You can submit one Referral Code per account, to be awarded 5 Diamonds. Go to the Options Menu and tap on the 'Submit Referral' button. If the Referral Code (another player's BBB ID/Friend Code) is valid, the Diamonds will be awarded after you tap the 'Submit' button. You will get the Diamonds immediately, and the referrer gets the Diamonds in 2-3 days. An account can only be referred a maximum of 5 times.