Learn Portuguese (Portugal): Amanhã nós voltamos para o nosso país.

This is the core difference between the two prepositions! We use para when going somewhere for a long time or permanently. Since they are returning to their home country, it is a long-term move. If they were just visiting for a short trip, they would use a.

The word Amanhã means 'tomorrow', so why is the verb voltamos in the present tense?

In Portuguese, you can use the present tense to talk about the future, as long as it is a planned event. Adding a time word like Amanhã makes it clear that it has not happened yet. We do this in English too, like saying 'We return tomorrow.'

Why is there an o before nosso país? Doesn't that mean 'the our country'?

Yes, literally it does! In European Portuguese, you almost always put a definite article (like o or a) before a possessive word. Because país is masculine and singular, we use o to match it.

What is the difference between país and pais?

The accent mark changes both the meaning and the pronunciation! país with the accent means 'country' and is pronounced as two syllables. Without the accent, pais means 'parents' and is pronounced as one syllable.