A transaction can only be completed and its record can be added to the blockchain once its accuracy and legal authenticity are checked—that’s done by a validator.
In the Proof-of-Stake mechanism, a validator determines whether or not a proposed ‘block’ conforms to the rules that deem it as valid. The entire process makes a blockchain network secure and transparent.
Unlike proof-of-work, validators don’t need to use significant amounts of computational power because they’re selected at random and aren’t competing. They just need to create blocks when chosen and validate proposed blocks when they’re not.