The Importance of Slang in English

If you talk to British people or you come to the UK, you'll probably hear lots of slang and they are quite hard to learn. I find often that if you look in the textbooks, or perhaps not textbooks, but if you look on websites, they're kind of often not very useful slang. They're maybe really old fashioned. Another example that you might know is the word bloody. Anything when annoyed, maybe like, bloody car won't start again. But to be honest, this is a little bit old fashioned now. Perhaps older people and adults, some adults would say this, but I've never heard a young person or someone in their twenties use bloody, to be honest.