Doing something face-to-face means it's happening in close proximity to another person. When you're meeting face-to-face with your teacher, the two of you are together and speaking directly to each other.
As an adverb or adjective, face-to-face describes in-person interactions. If you're frustrated with an issue in your city, you might demand a face-to-face conversation with the mayor. And if you have sad news to convey, don't send a text: "I wanted to tell you face-to-face that I killed your plant." Being forced to confront something difficult is another use for this word: "It was at the karaoke party that I came face-to-face with my inability to carry a tune."