A knowledge of some slang words is going to help you understand and appreciate British TV shows. You shouldn't just speak exclusively using slang because that's going to make it sound a bit weird. Some people, when they talk about British comedy, for example, say British comedy is strange, we don't understand it. I expect a lot of that is because of the specific bits of language which are used as well. Certain slang words and things might make British culture seem slightly bizarre, slightly foreign. Hopefully, understanding some slang can help to bridge that cultural gap and allow you to appreciate things like the British sense of humour and British TV shows  like that.