"I sometimes watch a movie at the movie theater."
It's the same particle used to say "I eat with chopsticks," おはしで食べます。
In English, this is sort of done in sentences like "I'd rather see Star Wars in the theatre." It's not specifying one location on the map, what you're really saying is you want the big screen and the surround sound and the popcorn and everything else that goes along with the theater experience, as opposed to seeing it at home.
You could also think of it as the difference between "We're at a restaurant" vs. "We're eating out." It's subtle, but they do convey two different things.
I'll try to stick to the location aspects of each particle, from what I've learned from various different online sources so far:
-by means of: by train, by bicycle, with chopsticks (by the use of chopsticks), in English (by means of using the English language -> speak/explain/talk to me in English = eigo DE o kudasai).
-a location where something is happening (eating at a restaurant, watching a movie at a theater, swimming at a VENUE such as the municipal pool or the olympic stadium, attending a concert at the budokan, basically any background location where an action is taking place, rather than you going to that location which is NI/HE).
-direction of movement (HE is more of a general direction, NI is towards something).
-NI is also used as a direct object in many cases, and it goes with many verbs where something is done/given to somebody. HE is not used for this.
-apart from being an indirect object marker where the thing is being used or something is being done to it ->->->
-in cases of movement it implies that the movement is THROUGH that particular spot as opposed to TOWARDS that particular spot (as in the sentence koen WO sampo shimasu which means strolling through the park, not walking all the way to the park/going for a walk to and until the park.)
I wrote the sentence as ときどきえいがかんでえいがを見ます which was marked as correct, but i can see that i have a slightly different order to the solution.
I think my solution is probably more literally "regarding movies, i watch them at the theatre sometimes" but just wanted to know if my Japanese would sound a bit unnatural?