Before a carnivorous plant can digest its dinner, it has to catch it. Carnivorous plants often give off a sweet aroma or produce nectar, which attracts insect. When the insects land on the carnivorous plants, they are trapped and digested. Some carnivorous plants such as the famous Venus flytrap have moving leaves that enclose their prey. Others use sticky surfaces, hairs which catch the prey or novel shapes to ensure the insects can't escape.
The majority of carnivorous plants use digestive enzymes to dissolve their prey. Venus flytraps, pitcher plants, honeydews and many other nepenthes begin secreting digestive juices inside their leaves as soon as an insect is trapped. These enzymes do not harm the leaves, but break down the protein in the insect's body until it can be absorbed by the plant. Some carnivorous plants do not produce the enzymes themselves, but have bacteria living in their leaves that digest their prey. Much like the bacteria in the human intestines, these bacteria help the plant absorb nourishment while the plant in turn gives them a habitat to live in. Certain plants even use both digestive enzymes and bacteria to digest their food, just like the human digestive system.
Some carnivorous plants actually use insects or larvae to do their digestion for them. South African Roridula plants have colonies of insects called Pameridea. These plants trap bugs, but do not digest them. That job is done by the Pameridea, which are not harmed by the plant. The Roridula plants digest the excrement of the bugs, which gives them nitrogen and other needed nutrients.