Hackers is a term used to describe a person or persons involved in illegally breaking the security of a business or account. Another term to describe this person is a 'Cracker'. Hacking is the other way around, and actually break in legally to find weaknesses and report them to the account/ business to help improve their online security.
There are several types of hackers, and they all do different things, you have the classic 'Black Hat' hacker, that illegally cracks accounts in order to gain something for themselves, money, perhaps. A hacker uses bugs (malicious scripts) to gain access to your device or to damage its normal operation.