Question(s) About Brute Forces Attacks

So on an online gaming forum that I sometimes read,

occasionally, someone writes on the forums that they've been "hacked", when really, they fell for a fake "Gimme your account info, and you'll get X amount of in-game money".

However, in a thread I read today, someone claimed that they got hacked because someone only knew their email for the account. My mind raised a question "was it a brute force?"

Meanwhile, the game's developers say that hacking the password is "Impossible". But from what I've learned so far, nothing is truly un-hackable.

So it brings me to my main question:

How do brute force attack programs/password-cracking programs (John the Ripper, Cain&Abel, THCHydra) work?

and do brute force attacks work on all types of logins? (I'm not asking this to try it, but rather because out of curiosity)

Thanks