A lot of times, I hear normal sentences without slang and sentences with slang. With my youth and inexperience with slang, it seems difficult for me to understand whether someone is using slang or not without asking the person. Other times, I assume the slang is normal and treat it as not slang until someone tells me that it is so.
So how can I easily differentiate slang from normal, non-slang words without having to ask or bring a book with slang phrases in it (which was recommended by a few friends)? This would also help improve my fluency within the language while adapting to the culture/community around me.