Laid back can have a positive or negative connotation depending on the context.
Bob's laid back management style creates a lax work environment where things don't get done on time. (negative)
Bob's laid back management style is the reason that his employees are so happy and productive. (positive)
I would say that this idiom is a little too slangy for a beginning English user to use comfortably. The range of interpretations can go from "lazy" to "comfortable."
Student or Learner