Characters, as you probably know, are the agents in a work of fiction that cause action and create conflict and drive plot. They are the personalities about whom we care, with whom our imaginations interact, who develop images and themes of life and living. In some instances, characters can be non-human creatures or, in rare instances, inanimate objects. The Wind in the Willows is an illustration of the first for it is peopled with moles, rats, badgers, toads. The House of the Seven Gables is an illustration of the second in which the house where Hepzibah lives is an integral part of all that occurs.
In "Hills Like White Elephants" there are two central characters, and one central character who is inferred though never introduced. There is one minor character who interacts with the first two and facilitates their interaction. There are characters who are mentioned and provide insight into the character of the American man but who have no discernible role in the action.
Coming back, he walked through the bar-room, where people waiting for the train were drinking. He drank an Anis at the bar and looked at the people. They were all waiting reasonably for the train.
The two central characters are the American man and his girlfriend who is the only one who has a name--she is called Jig.
The American and the girl with him sat at a table in the shade, outside the building. It was very hot and the express from Barcelona would come in forty minutes.
The character who is inferred is the unborn baby of Jig's pregnancy. The minor character is the woman who brings them their drinks through the symbolic beads that represent separation or dividedness. The other characters are the people in the "bar-room" who are "all waiting reasonably for the train."