Asking "How to claim free spins?" usually happens after a bonus has vanished, taking its winnings with it. The cause is almost always a condition in the terms: a deadline that passed, a withdrawal made too early, a cap on winnings or a clause about irregular play. Each of these can be seen in advance, and a short read of the terms shows which of them apply to any particular offer.
Requesting a withdrawal while a bonus is active often cancels the bonus and everything won with it, and some casinos apply the rule even to cash deposited alongside it. A player can usually cancel a bonus on purpose from the account page, which frees the cash balance at the cost of the bonus. Knowing where that option sits, and what it removes, turns an accidental forfeit into a choice made knowingly.
Casinos can change their bonus terms, and most promise that a bonus already claimed stays under the version accepted at the time. The promise matters only if the version can be shown, so saving the terms on the day an offer is taken is worth the minute it costs. The same goes for anything support agrees in chat: a saved copy of the conversation settles more disputes than anyone's memory of it.
Every bonus has a deadline, and usually two: one for claiming it and one for completing its wagering requirement. When the second passes, the bonus and any winnings still tied to it are removed, however close the requirement was to completion. Deadlines range from a day for free spin winnings to several weeks for a large match. The clock often starts at the deposit, which means a slow first session already uses part of the available time.
Usually not. Opening more than one account per person or household is a common abuse clause, and it can void the bonus and its winnings.
Usually from the account page. Doing so frees the cash balance but removes the bonus and whatever was won with it.
Casinos can revise their terms, though most promise that a bonus already claimed stays under the version the player accepted at that time.
Often yes. Asking to withdraw while a bonus is active can remove the bonus and its winnings, and some casinos apply this to the deposited cash too.
A saved copy of anything support agreed settles disputes far better than memory, especially if the promise is later questioned.