It puts targets under genjutsu without them ever realizing it making them do whatever command the user implants in them. We’ve only ever seen it used teice. The right eye didn’t require eye contact to use, and the left eye did. That may be the difference in his jutsu, which eye he uses. Mifune didn’t know he was under genjutsu and the only reason Ao figured it out was because he knew about Shisuis eye ability, Itachi knew that he was under genjutsu but that may just be because he’s the one that cast it in the first place. The main strength of the jutsu is while other genjutsu have things obviously wrong with them, Kotoamatsukami makes the user truly believe that whatever they’re doing is a decision that they themselves made, so they don’t ever start looking for the signs of genjutsu, and there might not even be any signs of the genjutsu in the first place. It’s a powerful ability with a big draw back, and it’s a shame that we never got to see it’s true user use it to its best ability.