Learn French: On va au stade pour un match demain. - We are going to the stadium for a game tomorrow.

Yes! In spoken French, the pronoun on is almost always used to mean "we". However, it follows the same grammatical rules as "he" (il) or "she" (elle), which is why it uses va (from the verb aller) instead of the formal "we" form (nous allons).

Why is it au stade instead of à le stade?

In French, the word à (to/at) and the masculine word le (the) always combine to form au. You will never see à le written together. Because stade (stadium) is a masculine word, "to the stadium" automatically becomes au stade.

Can we use the present tense verb va to talk about something happening tomorrow (demain)?

Yes. Just like in English ("We are going to the stadium tomorrow"), you can use the present tense in French to talk about an action that is already planned for the near future.

Why use pour here?

Pour simply means "for". In this sentence, it is used exactly as it is in English to show the reason or purpose of the trip: pour un match (for a game).