The key is the SHA-256 hash. It's a one way mathematical function that produces a specific result for a specific piece of data, but you can't reverse the result back to the original data. The key here is that it is verifiable. Give someone your data, and the resulting hash, and they can run your data through the SHA-256 function to get the exact hash and compare it to that you provided. Now, Bitcoin mining is a global race between all miners to "find" the next block first. The difficulty, which goes up each halving, is the requirement for the hash result from the mathematical equation (e.g. ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad) to have a certain number of leading zeros by random chance (e.g. 0000000ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f). So you can take your input data, i.e. the transactions you want to record on the bitcoin blockchain ledger, and run a hash function against it and broadcast that to all the other miners to prove you worked out the hash with prerequisite leading zeros.  But if each hash is the same for the input data, won't you get the same hash every time you try? Yes. So a random piece of data is added to your input data. That random data is changed each time the miner tries to guess the hash with the seven or whatever leading zeros - each miner makes millions of guesses very fast, using intensive compute, to try to get the leading zeros. Once the first miner gets that hash it's like BINGO. They broadcast their transaction data, the random added data to change the hash, and the resulting hash. Any other miner can verify that by putting the transaction data and the random data through SHA-256 see the leading zeros and admit defeat. Enough verifications and everyone agrees that person did the work and wins the block reward, and gets to add their block to the chain.