Some casinos, thanks to their software, offer players both real money games or the paid games and the free play or the practice version. Such casinos have a 'Play for Free' or a 'Practice' button in front of the games in the gallery, clicking the button allows player to explore the game interface and play it for free without any deposit. Any kind of winnings made in free games are not redeemable and either.
In certain casinos, there are free play options but only for specific games.