Several ways. Cats are the definitive host for toxoplasmosis, that is, the sexual life cycle for the organism takes place in their intestines. The oocysts are then passed in the stool and become infectious to humans after a few days of maturing. Many people, however, acquire toxoplasmosis by eating undercooked meat that contain cysts in the tissues rather than from cat droppings.
Cats. Cats are the host, handling infected cat's feces can infect humans too.