Private key and seed are two different types of keys that you can use to access your wallet. A private key is a password-protected string of numbers and letters that give you the ability to send coins from your wallet, while a seed is simply an encrypted version of this same set of numbers and letters. You can think of it like a password for your wallet, but without having to remember or type in any characters! This means that if you ever forget the private key or lose it then the only way to access your funds would be through using the seed.