How does the author make us feel sympathy for the characters?

There are only certain characters that we feel sorry for. These happen to be sympathetic characters to begin with. Shmuel is a sensitive little boy in a death camp; Bruno is an empathetic boy who must live with his father: the Nazi commander of the death camp; Pavel is an old man who prepares meals and waits on Bruno's family at Out-With: he is a former doctor who is very kind to Bruno. The reader is given a lot of reasons to connect with and care about these characters.

I don't understand!!!