Demo mode lets you play a slot with virtual credits instead of real money. It is useful for seeing how a game works, its features and its pace, before deciding whether to play it for real.
On GB-licensed gambling sites, since 7 May 2019, you must have your age and identity verified before you can play free demo versions, just as for real-money play. Some provider and information sites outside the casino environment show demos too.
A demo normally runs the same game as the real-money version, but short demo sessions say little about real results because of volatility. A few hundred spins can land a big feature or nothing at all. Demo results also feel different when no money is at stake. Use demos to learn the rules, not to judge whether a game "pays".