"To" is a small word with many meanings, but in this type of sentence it is like short for "towards" (in the direction of). You can think of it like an arrow pointing to the right. "He is respectful to customers" = "He is respectful -> customers" (he respects customers) "The customers are respectful to him" = "The customers are respectful -> him" (customers respect him) "She is speaking (to)-->him." (she says words, he hears them) You can use many examples with this pattern to tell who is doing what.