Learn Portuguese (Portugal): A que horas começa a aula?

In Portuguese, when asking what time an event happens, you use A que horas (literally "At what hours"). If you just ask Que horas são?, it means "What time is it right now?". Because you are asking when the class starts, you need the A to mean "at".

Why is "horas" plural if we are asking for one specific time?

In Portuguese, time on the clock is generally treated as plural (counting the "hours"). Because of this, the English phrase "what time" naturally translates to the plural que horas.

Why is the verb "começa" placed before "a aula"?

In Portuguese questions, it is very common to put the action (the verb) before the thing doing the action (the subject). Literally, this sentence asks "At what hours starts the class?". However, you can also keep the regular order and ask A que horas a aula começa? — both are perfectly correct!

I thought "class" was "classe". Why use "aula"?

The word aula refers to the actual lesson or period of instruction (like a math class or a Portuguese lesson). The word classe usually refers to the group of students themselves, or a category (like "first class" on an airplane). Since you want to know when the lesson itself begins, aula is the right word.