All you need to do is maintain a balance of at least 30,000 satoshi (0.0003 BTC) in your FreeBitco.in account and they will pay you compounded interest on your full balance everyday (at a random time of the day).
There is no lock-in period to earn interest (you start earning interest right from the first day!) and your balance can be withdrawn any time you wish. Treat your FreeBitco.in account like an instant-access savings account to hold your excess bitcoins and earn passive interest on your account balance everyday.
Additionally they offer you the chance every hour at absolutely no risk to earn up to $200USD worth of bitcoin by simply taking advantage of a free spin every hour.
Now is this a scam is most likely your next question. and with the number of scam tokens / sites / wallets out there, a valid one. I personally have been using this since 2017 and below are some proof images of that, and that i have managed to withdraw without any issue:
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