Ampulla of Vater
Illuminator
Without knowing how clued up you are on the technicalities of the internet I don't know what level of detail to go into.
The blockchain is a "distributed" network meaning that each miner stores a copy of it on their computer.
When an individual initiates a wallet transaction let's say that this transaction is "broadcast". Each miner can then read and validate the transaction. Part of the validation is going through your copy of the blockchain to verify that the individual has enough bitcoins to make the transaction (this eliminates "double spending"). Once a miner assembles a block and generates the correct "nonce", they "broadcast" the block. The other miners then read it and once they verify that it is a valid block (and that all the transactions in it are valid), they add it to their copy of the blockchain.
There are many technicalities involved including how to deal with "forks" (where 2 or more miners broadcast a valid block at the same time) but you will need to look up a more technical website if that is the sort of detail you are looking for.
I guess maybe like peer to peer or the old Napster. Or tor. Maybe not. As I think about it there was no need for everyone to have the same files on their computers. If someone dropped offline during a download, it immediately picked up from someone else's copy, but that was different than what you are saying. I do understand this explanation. Thanks. Every little bit helps.