I have dark skin patches on my feed, some seems like they are fading away but some are very dark and looks like a dead cell?

Get diagnosed. I assume you mean feet.Various problems possible.Could be fungal,eczema or other(dry skin?).Best to get visually assessed by your doctor.In meantime,start with a good moisturiser.People tend to neglect feet care,concentrating rather on body parts revealed to the outside world.
Go well. Maintain good hydration and a balanced diet.
Could be a problem. A difficult question to answer without more info or a picture. Could be superficial inflammation or even melanoma or compromised blood flow. Always best to get strange skin conditions looked at by a professional.