What a private key does
A private key is secret cryptographic information used to authorize actions for an address. The exact implementation differs by wallet and blockchain, but the security principle is simple: anyone who gains control of the relevant secret may be able to authorize transactions.
Public address vs private key
A public address can normally be shared to receive funds. A private key must remain secret. Confusing these two is a common beginner mistake. Sharing a receiving address is not the same as sharing the secret needed to control funds.
Why screenshots are dangerous
Screenshots, cloud backups, email drafts and messaging apps can expose secrets to other accounts or devices. Recovery information should be handled according to the wallet’s documented backup method and kept away from ordinary online storage.
Signing is not the same as sending blindly
A wallet may use a private key to sign a transaction without revealing the key itself. Users should still inspect the destination, amount and network before approving. A secure key can still be used to authorize a malicious transaction if the user approves the wrong details.