Most hash functions (SHA-256, MD5) are designed to be fast. That's bad for password storage: attackers with stolen hashes can try billions of guesses per second.
bcrypt is intentionally slow, and you can dial up the slowness with a 'cost factor' as hardware gets faster. A cost of 12 means roughly 4,096 hash rounds per password.
It also salts passwords automatically, each hash includes a random salt, so the same password produces different hashes for different users.