White hat hacking

What I know
I really don't know anything about this topic, I obviously know that is a form of hacking but i don't know how it works or what they do.

Questions I have about the topic
1. Why is is called White hat hacking?
2. How is it different from normal hacking?

Links with useful info
http://searchsecurity.techtarget.com/definition/white-hat
http://searchsecurity.techtarget.com/definition/black-hat
http://www.cyberlawsindia.net/grey-hat.html
http://www.secpoint.com/What-is-a-White-Hat.html

Things I learned
- White hats are people who hack a website to show its flaws to the owner just in time so they can fix the problems. They are against the abuse of computer systems.
-They are security specialists that test a companies website by making tests, examining the system and analyzing. Most of them are employees that work for the same companies.   
- They are the opposite of black hats. Black hats are the hackers who hack a web page trying to damage it and revel confident information.
-The name comes from the concept in movies that bad guys used black hats, to be the opposite, good guys wear white hats.
-Also there exist Grey Hats. These hackers are not good as white hats or bad as black hats, they are in the middle and usually don't hack for personal purposes.
-White hats have many names, some of them are sneakers, white knights, ethical hackers and more.
- They need to have an certificate for doing what they do that is given by the NSA, the National Security Agency.

How it relates to my life
It could relate to my life in the future. Maybe when I grow up I am going to work in an important company.  It is useful to know that there are specialized hackers that could help to improve security and end up benefiting lots of persons.

Questions I still have 
I still want to know how do hackers do the hacking?