The algorithm that concurrently secures the Bitcoin blockchain, orders transactions into blocks, facilitates consensus, and enables new bitcoin to be minted through the block subsidy. In PoW, Bitcoin miners compete to find a qualifying block hash using computing power, which is measured in hashrate. The first Bitcoin miner to solve the block is rewarded with bitcoin (plus transaction fees) and wins the right to update the blockchain.
More technically, miners must find a numeric solution to the SHA-256 algorithm that meets a network-wide difficulty target. The only way to find that solution is repeated brute-force guessing, so every valid block represents real energy spent, while any node can verify the finished solution instantly.
