How to Use a Blockchain to Mine Bitcoin

In a new transaction, you have a wallet, say the Bitcoin Core wallet. You enter a destination and an amount and then what it's going to do is It's going to look for coins. Those are inputs basically that add up to at least the amount you need to spend... Then that's a change to go back to you. Now let's say you want to be safe and you want to put your private keys not on your computer but in a hardware wallet. But what about those inputs? I know nothing about them. So here's the problem. The amount was already in the blockchain from the previous transaction. You're just spending the coins from that transaction and the only thing you