Summarize:

If you keep your Venus flytrap outside, it will catch spiders and insects on its own (unless your outdoor environment is unnaturally sterile). When you see the leaves in a clasped position, the Venus flytrap has probably caught something. If you want to feed the Venus flytrap - either because you're keeping it indoors or you just want to experience the excitement of watching it eat - you can use mealworms, insects or spiders that are small enough to fit in the leaf traps. Place the food inside one of the traps or release it inside the terrarium. The trap will close when the tiny hairs inside are triggered by the insect's movements. It's best to feed a Venus flytrap live bugs. The plant won't close unless it senses movement, so feeding the plant dead bugs is not a good idea. You can purchase live or dead insects from a pet store, but you could also try catching your own. For smaller Venus flytraps, black flies are a good size. For larger traps, you could try small crickets. Venus flytraps can go months without eating, but if you're keeping yours indoors you should plan to feed it about once a month for best results. Once the Venus flytrap closes over its food, it takes at least 12 hours to digest its meal. Digestive enzymes break down the soft inner fluids of the insect or spider, leaving the exoskeleton intact. After about 12 hours, the trap will open and the empty exoskeleton will blow or wash away. If a small stone or another indigestible object ends up in the trap, it will release the object after 12 hours. You might be tempted to give the Venus flytrap a piece of ham or chicken, however, the plant does not have the right enzymes to digest animal meat. Feeding it anything besides spiders or insects could cause it to rot and die.
Let the Venus flytrap catch its food. Feed the Venus flytrap mealworms or insects. Watch for the trap to reopen. Don't feed it meat.