Student or Learner
1. What do I describe words of phrases which are for common use during conversation but they are not slangs.
2. Should I put slangs the plural form as there is a single word which stands for one meaning?
3. Is the above sentence correct?
I think the answer to your first question, Ju, is colloquialisms, or colloquial words or expressions. That is, if you're asking about words or expressions that are used in speech but not in formal writing.