Learn Portuguese (Portugal): A que horas vamos ao parque?

In Portuguese, you often drop the subject pronoun because the verb form already tells you who is acting. The verb vamos is the "we" form of the irregular verb ir (to go), so the word nós (we) is unnecessary here.

Can vamos mean both "we go" and "we are going"?

Yes! The Portuguese present tense covers both the simple present (we go) and the present continuous (we are going). You rely on context to know which one makes the most sense. Here, it is used to talk about a near-future plan.

Why is there an A at the beginning of the sentence?

When you want to ask "At what time" an event happens, you must include the preposition a (at) before que horas. If you simply ask Que horas são? without the a, you are asking "What time is it right now?".

Why do we use ao instead of just a before parque?

The word ao is a mandatory contraction of the preposition a (to) and the masculine definite article o (the). Since parque is a masculine noun, they combine to mean "to the". If the destination were feminine, like escola (school), you would use the feminine contraction à.