Free spins, no deposit bonuses all have a slew of laws and regulations that you can include in their terms and conditions (T&Cs). These are non-negotiable and govern how the free spins would be utilised. In other words, if you deviate from or violate them, your payment will most likely be revoked.
The wagering requirement is the most relevant law or T&C. This is the smallest number of times your free spins winnings to be wagered or played out before you can cash them out. Another rule is that you should only play those games. Most casinos want you to use your free spins on one or a few specific games.