Watch, read and listen widely. It would be a mistake to think that one single TV show can give you a clear understanding of English!
And a caveat: slang is always highly cultural and regional. It's not a fast-track to good English. And like XiaoHei says, slang is not universally understood. I still have to check the occasional Americanism I hear, and if I started using them I'd sound like an outsider to both Americans and Australians - even if both groups could understand the words I'm saying.
If you want to use slang, limit it to your own English-speaking friends,and use it only after you hear them use it. :)