Your text is converted to bytes using UTF-8 encoding — every character becomes a number.
The bytes run through a one-way mathematical function. Even a single character change produces a completely different output.
SHA-256 and SHA-512 use the WebCrypto API — cryptographically secure and standardized.
MD5 and SHA-1 are deprecated for security — use SHA-256 or SHA-512 for passwords, certificates, and integrity checks.