Hi all

This is pretty basic, so I apologise about that but it is something I have failed to find an answer to so far (probably just looking in the wrong places.)

Anyway, my question is this, at what exact stage does a new block get formed in the Bitcoin blockchain and how? In my research it seemed to say that a new block is formed once a miner solves the required "puzzle". From what I read, the puzzle is the first solution to a specific SHA-256 hash of the current blocks contents plus a nonce that generates a specific number of leading zeros. I understood once that is solved, a new block is created, the successful miner is rewarded and new transactions will then be written to the new block. That all seems fine (as long as my understanding is correct.)

What I do not understand in the above process, the hashing of the current block surely only works if the data inside the block is complete and unchanging. If the data is changing the data hash would keep changing. But surely if a new transaction is made, new data is being added to the block and that data is causing the hash to change.

Can anyone please set me straight on what I have wrong or am missing.

Thanks