An explicative and an expletive are two similar words with very different meanings which can be easily confused when in the flow of writing.
An explicative serves as an explanation of something; for instance you may be studying an article which comes with some additional explicative material.
Whereas, an expletive serves quiet a different purpose.
An expletive is any word or phrase which is meaningless in terms of expanding on the meaning of the sentence and is simply acting as “filler”. It is more commonly recognised as an oath or swear word, exclamatory, obscene or profane.