What's "do a favor" mean and when's it used?
Answer from a Native speaker
To "do [someone] a favor" means to do a kind and helpful act for someone beyond what is expected. You can use it when you ask someone for help with something or if someone does something kind for you that you needed help with. Ex: Can you do me a favor and call the restaurant for me? We need to book a table. Ex: She did us a huge favor by helping us move last weekend. Ex: A: Hey! Can I ask you a favor? B: Sure, what is it?