A private key is a 64-bit long hexadecimal string consisting of letters and numbers. After you create a wallet, you can export the private key by entering the password, and there is only one private key for a wallet and it cannot be modified. Usually, the private key and the public key appear in pairs in a wallet. With the private key, you can generate the public key through a certain algorithm, and then generate the address through the public key through a certain algorithm, and this process is irreversible. In any mainstream wallet, you can import the assets from the previous A wallet into the B wallet by importing the private key and setting a new password. For example, if you lose your phone, you can recover the assets by simply importing the private key. Please note: Whoever has the private key has control of the digital currency. So the private key is very critical and must be kept well.
A seed phrase is a collection of words that can be used to access your crypto wallet.
The seed phrase is another form of the private key. The seed phrase is created because the private key consists of a 64-bit string, which is not convenient to record and is easy to copy. The main purpose is to let users remember their private keys better. After creating a wallet, users need to back up the seed phrase(12 words), and each word has a space between them. The seed phrase has the same function as the private key, i.e. it can be imported into any mainstream wallet by entering the mnemonic and setting a new password. Like the private key, a wallet has only one set of tokens and they cannot be modified.