When you mine Bitcoin, your computer will create a new block (set of transactions) with the latest transactions, and calculate a unique number called hash. If you calculate the hash of the same thing twice, you will get the same hash. If this number is under a target difficulty, the block is then sent to a node that validates the block and broadcast it to other nodes. If it is not under the target difficulty, a value in the block called the nonce will be changed and the computer will retry with the new block. Hope I helped! Did I miss anything?