Imagine you have a combination lock with 4 digits. If you wack your head against a car hood by accident and forget the combination, this means you have a problem with 255 wrong answers and 1 right one. If you had a few days to spare, you could try all of them. The marvelous thing about computers is that they can, quite easily, auto-generate all 256 possibilities and beat the lock senseless with them. Until it opens.
That’s a brute force attack.