Slang isn't global English, and might not be understood by non-native speakers.
Most people learning English will likely be using a global version of the language.
Slang expressions might be confusing for non-native speakers depending on their level of English.
The use of slang is optional, but is common in TV shows, song lyrics, books, and among English friends and colleagues.
Finally, here is the third part of this series about English slang words and expressions that most British people know, but which will probably confuse almost everyone else! I started this series in 2019. It's only taken me nearly 4 years to get round to finishing it. Learn loads of slang and culture, plus a bit of British history too.