Before anything else, you should restart your phone to see if that fixes it. Sometimes all your phone needs is a good restart. If it doesn't you have you will have to open up your device. Having something stuck inside the lens seems unlikely since the phone is sealed, but it is possible. You want to open up your device following this guide. Once you get to the camera, check to see if there is anything stuck in the case. If there is none, get the camera itself for damage and scratches. If you notice a scratch on the lens, you'll need to replace it.
There is a guide on ifixit found here During the initial breakdown, we also stripped several screws.We found that using elastics was ineffective as the driver heads were small enough to just puncture the elastic. We found that using a rotary tool to create a slit for a flat head screw driver worked best. However this is a little risky and should only be done as a last resort.
It sounds like your issue could be your battery or charging port. Check to see if there are any obstructions in your charging port. If there are, carefully remove any obstructions with compressed air, or using a brush. If your charging cable does not fit properly in the port, then your charging port could be damaged. It will need replacement. If that is not the case, you may have a bad battery. Check to make sure your battery is connected properly. Ultimately you may need to replace it. Follow this guide to replace it.