Imagine you are a tourist in a country whose language you do not speak. In a restaurant, you hand over a credit card to pay for the bill, but the server seems to say something apologetic in response. Even though you don't understand his words, you can probably conclude that the restaurant doesn't take credit cards, and you need to pay with cash instead.
This is the technique of inferring meaning: using clues and prior knowledge about a situation to work out the meaning of what we hear.
Similarly, we can infer the relationship between people from the words they use, without having to find out directly. Take the following conversation:
A: Tom, did you do your homework?
B: I did, sir, but the dog ate it.
A: That's a terrible excuse. You'll never pass your exams if you don't work harder.
We can infer from the use of the words 'homework' and 'exams' that this is a conversation between a student and his teacher. By using contextual clues and our knowledge of the world, we can work out what's being said, who is speaking and what's taking place.