You need to have all of your seed phrases in order to gain access to your wallet, for anyone to see. If someone steals a few of your seed phrases, you probably won't be harmed. A good way to store your seed phrase is to engrave it on a piece of stone or metal, as it won't get wet or burn in fire.

For extra security, you can create a passphrase along with your seed phrase. This gives you more security and is easy to remember. The biggest advantage of securing your wallet with a passphrase is that even if your seed phrase is stolen, if the thief doesn't know the passphrase, your wallet's seed phrase will be considered useless. You won't get the passphrase feature on all wallets. Some hardware wallets like Ledger, Trezor, and Electrum do offer this security feature, although the Electrum Bitcoin Wallet does. The passphrase is also called the 25th or 13th word. So always save it separately from the seed phrase or set it to a sentence that you will always remember.