BIP39 is the standard most wallets use to turn random data into a human-readable seed phrase of 12 or 24 words from a fixed list of 2,048.
A checksum is built in so wallets can catch many typos. The same words restore the same keys in any compatible wallet. An optional passphrase (the "25th word") creates a completely different wallet from the same words.
Anyone with the words can spend the coins. Never type them into a website or photograph them.