I feel useless and depressed. What are you supposed to do when you feel like your life has no meaning or purpose? I've tried getting a job and that didn't help.

Take a hobby class or join a club. Do something you enjoy or are interested in. Take up some sort of exercise, even if it just walking. Exercise releases endorphins which are mood enhancers. And if you can take that walk in a natural setting, such as a park. That also releases endorphins. If that doesn't help, see your doctor. Sometimes there is a medical reason. Your doctor can help with medication.