"Where do we start?"
Translation:Kie ni komencas?
-ien correlatives mark motion, while -ie correlatives mark location. Other correlatives (e.g. kio) still take the accusative when they would normally take the accusative. http://donh.best.vwh.net/Esperanto/correlatives.html
That website has always put a bad taste in my mouth and unfortunately they are too many Esperanto speakers with the same attitude.
"The correlatives are the bete noir of many English-speaking students of Esperanto; they never seem to get them right. This is, in my opinion, a simple lack of diligence on their part; even memorizing the fifty words separately should take no more than the better part of an evening. "
In other words, if you get them mixed up or wrong you are an idiot.
Well... If we were classes wanting to start in a school, we would say that :D But normally we only start something (we start eating, we start sleeping, we start making, we start going...). "Komencigxi" is for the other meaning of "start" (the TV show started, a new age starts...)