Це can be used in 2 meanings. It's mainly used as a free-standing pronoun ('it', 'this') when it doesn't modify a noun:
- Це я. It's me.
- Це комп'ю́тер. It's a computer.
- Це кінотеа́тр. This is a cinema.
Цей is used like an adjective, it modifies some noun:
- цей кінотеа́тр 'this cinema'
- цей комп'ютер 'this computer'
Цей is only used before masculine nouns. (Ukrainian nouns are divided into 3 genders: masculine, feminine and neuter.)
Before feminine nouns, you use ця:
- ця шко́ла 'this school'
- ця вчи́телька 'this teacher'
And before neuter nouns, you use це. This is the second use of це:
- це молоко́ 'this milk'
- це ім'я 'this name'
Since це can be a free-standing pronoun and a neuter modifier, sometimes sentences can have 2 meanings. But only with neuter nouns:
- Це сонце. This is sun. OR This sun.
Hope that helps.
There is a difference here.
"Кіно" means "cinema" in the sense of the building, the location only in sentences like "Я в кіно" or "Я йду в кіно". If you simply ask "Де кіно?" that does not means "Where's the movie theater", it means "Where's the movie?"
Should Duolingo also accept "Where is this theater?" I've reported it, just in case.
I think we decided that "theater" and "cinema/movie theater" are not interchangeable in this course. Unclear whether the user is confusing words or is aware of the meaning of the word and just being lazy :')