A book lung has a stack of soft plates called lamellae. Oxygen in the air passing between the lamellae diffuses through the tissue into the blood. Other spiders have tracheae which are breathing tubes held open by rings of chitin. The tracheae open to the outside and the opening is called a spiracle. There appears to be no active, muscular breathing mechanism.
Air seems to pass in and out of the book lung or the tracheae in a passive manner.
Relatively few spiders bite people because they are not able to pierce the skin with their fangs. The majority of those spiders that can bite people have venom that is harmless to people. Two notable exceptions in the United States are the Brown Recluse, and the Black Widow. When dealing with the effect of spider venom on humans there are two types. The black widow venom is neurotoxic.