is just a pair of keys - public is for others to send you BTC, private is for sending BTC to others.
Paper wallet - should be spent once, because of change, and anyway after using a computer to spend the coins make this paper wallet unsecure.
When spending from a wallet, the change is sent to a new wallet? So paper wallets are tricky, always spend the full amount to a normal wallet, then from there send change to a new paper wallet. Like in fiat money, you can't spend a part of a banknote. So clients send the remainder of the transaction to the original wallet.
When you come to use your paper wallet, empty it all into your live wallet then put the stuff you want kept safe into a new paper wallet.
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