Uninflected words are never inflected. But each is used slightly differently. Here are some examples of uninflected words.
api
api means "also." At the beginning of a sentence, it indicates a yes-or-no question.
ca
ca means "and." It comes at the end of a list of words. If it is repeated, it has the sense of "both … and."
saha
saha means "together" or "with." It follows a nominal word in the third case (gajena saha, "with the elephant").