You create a so called Genesis block on which everything is based. Maybe include a timestamp (in case of Bitcoin a newspaper headline) to prove that you didn't

You create a so called Genesis block on which everything is based. Maybe include a timestamp (in case of Bitcoin a newspaper headline) to prove that you didn't pre-mine and you are done. The Genesis block is then distributed with each implementation for bootstrapping the verification process. You calculate the hash of each block (which includes the hash of the previous block) and check if it matches the hash in the next block. Each block also includes the difficulty of the network at the time to prevent mining more than x block per hour. The difficulty describes the "format" of the hash of each block, e.g. the hash in hex format needs to have 50 times 0 at the beginning.