"My brother wants to go to the movies tomorrow."
Translation:Mi hermano quiere ir al cine mañana.
"Cine" is indeed "cinema", but when you say "go to the movies" in English, it's just an expression for "go to to the cinema". That expression, if you translate it literally to Spanish, would be "las películas" like you said, but it doesn't make much sense, simply because that's not an expression we use. So you must go with "ir al cine".
Maybe in Britain they would say something similar to "go to the cinema", since they use "films" instead of "movies", and "go to the films" doesn't sound quite familiar to me. Anyway, what matters is that "go to the movies" means "ir al cine" in Spanish. The literal translation "ir a las películas" doesn't make much sense.
You can't conjugate both verbs. You only conjugate the verb "querer", because "mi hermano" is the one performing the action. The thing he wants, ie, go to the movies, should not be conjugated, so you say "ir al cine" instead of "va al cine". Think of it in English. You don't say "My bro wants to GOES to the movie". You don't conjugate the "go" in that case, you just do it for "want".
I am ready to tear my hair out. I have submitted "Mi hermano quiere al cine manana." and been told that the correct answer should be "al cinema". After repeatedly reporting it, I give in and submit the requested, "Mi hermano quiere ir al cinema ..." only to end up here. ARGG
I figured out that I was writing, "a manana" but the bot was underlining the "al cine" part as the error so I didn't catch it.