First thing, this skill will get you to get into someone's account in any website including friendster, myspace, facebook (wooot!), yahoo mail or any account in any websites. And yes, you can also hack me if you like :P
Second thing is, you have to know that people's minds are unique. They can variably make passwords that nobody will ever think about, or they can also have passwords that people can guess easily. For example, they can make password with the name of their crush, or simply put abc123. You might think this hilarious, but there is a lot of people has it. I, myself have hacked accounts with that abc123-password.. but it's other skill of hacking that I will not state it here :> but mostly, it's mule account in gaming sites to keep their extra items/equipments, or as a spy in social community webby like fs, ms or fb (again, wooot!).
Thirdly, you have to have a target you want to hack. Someone you know closely or someone you don't even know or meet in real life, but close in community webby like portals. Get to know their interests, what they like: their favorite food or artist, what they are into like gaming, love? (yuck), computer, tv dramas, etc.
Fourthly, damn, just ask their passwords, if they give then you get it and enjoy. But then if they dont, LOL cannot is cannot la. HAHAHA why would people want to hack lol tho I used to be a hacker too xD