Learn Hardcore Japanese: kyuujitsu ni eigakan de eiga o mimasu. - I watch a movie at the movie theater on my day off.

Using 休日に marks on a day off as a time phrase. 休日は would instead make 休日 the topic, as in As for days off, …, often implying contrast or a general statement.

Why is the location 映画館 marked with で instead of に?

Particle で indicates the place where an action takes place. Particle に for location usually means existence or destination. Here you’re performing the action of watching at the cinema, so you use で.

Why is 映画 marked with を?

Particle を marks the direct object of the verb. Since 映画 is what you watch with 見る, it takes を.

Can I drop 映画 and just say 映画館で見ます?

Yes. If the context makes clear that you’re watching a movie, you can omit 映画 entirely: 休日に映画館で見ます.

Why is the verb in polite form (見ます)?

This is simply the polite (masu-form) in present/future tense. You can switch to the plain form 見る to be more casual, for example: 休日に映画館で映画を見る.

Why is the subject missing? Who is doing the watching?

Japanese often omits the subject when it’s clear from context. Here it’s implied that I (the speaker) am watching. You can add 私は at the start if you need to be explicit.

Why is the word order 休日に → 映画館で → 映画を → 見ます?

Japanese typically places adverbial phrases before the verb. The usual order is time (休日に), then place (映画館で), then object (映画を), and finally the verb (見ます).

What’s the difference between 休日 and 休み?

Both mean rest/break, but 休日 usually refers to official or scheduled days off (like weekends or public holidays). 休み is a broader term for a break or vacation, and can refer to shorter rests as well.

Can I specify a particular day like 土曜日に instead of 休日に?

Yes. Just replace 休日に with 土曜日に to mean on Saturday: 土曜日に映画館で映画を見ます.