The only way to start earning instant rakeback is through the VIP program. Once you have wagered enough to earn 500 XP you'll be promoted to Bronze 1.
At Bronze 1, the Instant Rakeback bonus automatically unlocks and you will earn a percentage of the rake on every single bet made through Degens thereafter. Every single bet, win or lose, will earn you an Instant Rakeback bonus.
To access your Instant Rakeback, just navigate to the VIP page and claim it there.
All the Instant Rakeback you've accumulated during your time at Degens can be claimed whenever you choose.