Why is my Camera not functioning?

Cracked lens

If you take multiple different photos and there is a discrepancy in the same spot in every photo, then there is probably physical damage to your lens. The damage/debris is obviously in the same spot every time, which lets you know there is a scratch/damage/debris on the lens. This is most likely irreparable and needs replacement.

Damaged internal sensors

If you open up the camera app and get a black screen or if you try to take a photo and the camera is unresponsive/not working, then there could be damage to the hardware or software portion of the phone that relates to the camera. Try closing background apps, restarting the phone, or backup data and do a factory reset. These methods should rule out any basic software malfunctions. If nothing is working, then there could possibly be internal damage to the camera's hardware. This would most likely require replacement.