Right after death your heart is no longer pumping so no blood is flowing through your body and reaches your brain.
So your brain cells begin to die as a result of the lack of oxygenated blood or any blood at all.
And immediately after death your body begins to cool down until the body reaches room temperature and when that happens it's known as Algor Mortis.
After Algor Mortis occurs then Rigor Mortis sets in around 4 to 6 hours after death where your body begins to get stiffer and stiffer until it's very hard to move the body easily.
A lot of skin cells have died after death of the body but some skin cells can still live for a few days after the persons death and then decomposition sets in and the body begins decomposing a few days to a week after death.
Usually a few days after death if the body is not embalmed the body starts decomposing and smelling bad.