How does change address interact with original address
There is no relation at all between the two addresses, except that they're owned by the same person/wallet.
At the protocol level, &quot;change&quot; does not exist. It's just another output (with a corresponding address), indistinguishable from normal &quot;payment&quot; outputs. It is your wallet that's creating it: it needs a place to send the remainder of a spent UTXO of yours that you don't actually want to transfer, so it creates a new address of its own (just like you'd do when receiving funds), and sends the remainder there. And it stays there, until there is a need to spend those funds. It could send them back to the same address, but this would be a serious privacy leak (it lets people distinguish change from payment), and have no cost advantage.