It's used in casual conversations with friends, family, and people you know well.
Here are some examples:
* "Tu és brasileiro?" (Are you Brazilian?)
* "Tu gosta de música?" (Do you like music?)
* "Tu podes me ajudar?" (Can you help me?)
Important Note: While "tu" is common in casual speech, in more formal contexts, it's better to use "você" (the formal singular "you").