It is a great question to ask by all novices. Never be intimidated by people who know from not asking them.
Ahemm. You received the 'proper' answers but mine is short and blunt.

Shorting is selling what you do not have with the hope that eventually you will make good on the transaction. In most other environments it is simply called 'commiting fraud', if only temporarily, but in stocks you are allowed by these means to gamble.

So it is a method to gamble without going to a casino. If it was up to me I would make it illegal.
So grass hopper, hope that augments your education.
Cheers and stay away from this method. Ed.