Monero addresses and keys are represented by strings of text. It is essential to understand these terms:
Mnemonic seed: Recovers a Monero wallet. Sharing it will allow anyone to access your funds.
Secret spend key: spends Monero and signs transactions. Sharing it will allow anyone to access your funds.
Secret view key: displays address data. Sharing it will reduce your privacy but will not allow anyone to access your funds.
Main address: receives Monero sent by another user (or exchange). It is safe to share this address.
Subaddress: a disposable address that directs funds to a main address. It is safe to share these addresses, and they provide extra privacy.
Wallets generally handle other incidental key and address information automatically. The most important thing to remember is that secret keys and mnemonic seeds should be kept secret, and should not be revealed to anyone. Failure to protect this information can result in a total and irrecoverable loss of funds.