A seed phrase is a human-readable backup of the private keys that control your bitcoin — usually 12 or 24 words. Anyone who has your seed phrase can spend your funds, and anyone who loses it with no backup can lose access permanently. It's the single most important piece of paper (or metal) in this whole setup.
A hardware wallet keeps your private keys on a dedicated, offline device, so they're never exposed to an internet-connected computer even when you're signing a transaction. It's the difference between your keys living somewhere a hacker could theoretically reach, and somewhere they can't.
A Lightning channel is a direct payment relationship between your node and another node, funded with an on-chain transaction. Once it's open, you can send and receive near-instant, low-fee payments back and forth without touching the blockchain for every transaction.
Put together: your node verifies the network, your keys stay in your control, and Lightning channels give you a fast way to spend — all without handing custody to an exchange or a custodian.