I would like to take a time-lapse of a sunrise/sunset with my Nikon Coolpix I820. What settings should I use?
This isn't possible in-camera. The L820 has no intervalometer (ability to take images at set intervals, e.g., every 10 seconds), and there is no shutter cable release port for you to use an external intervalometer. You can take a video and manipulate it in post production to speed it up or drop frames, but the L820 has no timelapse capability.