Security, transaction validation, and new ADA tokens are all made possible through the Proof-of-Stake consensus algorithm called Ouroboros.
The time is segmented by Ouroboros into epochs and slots, with epochs being the more comprehensive time frames and slots being the 20-second increments that are contained within epochs. A leader (stake pool) is selected at random to represent each slot, and this leader is accountable for selecting the blocks that will be added to the blockchain.