In order to receive your sign up bonus you have to do three things: register at a casino, select a payment method and make your first deposit. The sign up bonus will be credited to your balance immediately.
Some bonuses do not require a deposit. Take for example the free cash bonus (usually a nice amount): a bonus to play with within a certain time limit, for example an hour. You can keep the winnings. A so-called no deposit bonus is a similar kind of bonus: you get a small start amount to play with. Free spins are free turns on slot machines.
Many casinos give away a deposit bonus for new players. But the bonus conditions depend on the country from where you are playing. Therefore, carefully review the bonus conditions of a casino before you sign up.
Yes, at most casinos a time limit applies to the bonus. The period of validity of a bonus promotion depends on the type of bonus. The validity for sign-up bonuses is often around 90 days. Free spins are often valid for a shorter period, for example for a few days or 24 hours. Bonus promotions related to a public holiday or seasonal activity must also be used within a certain time. Make sure you always check bonus conditions of online casinos.