hi Crissorrir
 I think we use conversationally to describe the way we do something as
Ex. I always teach speaking skill conversationally. 
here conversationally is an adverb that describes the way I teach speaking. So if we want to be sure, we have to ask ourselves this question
How do you always teach speaking skill? The answer is Conversationally
 
 But conversational is an adjective, we use it to describe the thing itself as
Ex. conversational speaking skill is an important methed to be used in English classes.