Cardano is a delegated proof of stake (PoS) blockchain, so an ADA holder has a right to earn rewards by delegating their ADA to a stake pool. These rewards are minted as additional supply of ADA and added to the circulation.
Participation in Cardano stake pool LEGA enables you and other delegators to join and unite your assets as a way to increase your chances of being rewarded. Stake delegation allows you to participate on the Cardano network even if you do not have any skills in operating a validator node.
In simple terms, everyone delegates their staking power in the process of verifying and validating new blocks, so they have a higher probability of earning the rewards.