A passphrase is different from your 12-24 word seed phrase. It is an optional, advanced security feature that allows you to create a new wallet by adding an additional word to a 12-24 seed phrase. It is supported by many wallets utilizing the BIP39 standard.
Most popular cryptocurrency wallets use the BIP39 standard: the use of mnemonics to serve as your back up recovery seed in the event your wallet becomes compromised. This is also known as a mnemonic seed phrase, recovery seed, wallet back up, etc.
You purchased some bitcoin on an exchange. You want to take the next step and take control of your keys by withdrawing your bitcoin on a wallet you own. Here's the absolute minimum you should do to get started.