Most tarantula feed on live insects. Specimens that are growing larger can feast on small reptiles or even small mammals like mice, small lizards, and so on. Some tarantulas, when hungry, will wait their pray at their hide entrance. Others are stalking their pray to capture them in speed of light.
Tarantulas do not eat their food, they rather absorb it. From the beginning, they must prepare food for intake by injecting poison (digestive toxin) from their fangs into their prey. After the poison has liquefied the victim, only then will the tarantula begin to slowly absorb the food. The belly system of Tarantula is like a long tube that runs through the whole body. When food is ingested by the tarantula the food system breaks it down and then it is ingested by the tarantula in the body.
Tarantulas, like humans, are good to be fed by a variety of food: insects, cockroaches, worms, lizards and even mice for larger tarantulas. A hungry tarantula will be ready to attack a pray of it's size, just remember that you should not be given more food than the body of the tarantula (excluding the legs). Food that is not eaten within 24 hours must be taken out, as sometimes the hunter himself can become prey, but food leftovers can start to rot. I usually feed my spiders once a week, I give up to three cockroaches a meal to juveniles and adults, I usually feed spiderlings only one or two newborn cockroaches once a week.