Vitamin B12 is a water-soluble vitamin. It can dissolve in water. It is one of the B-complex vitamins. The B complex includes:

B1
B2
B6
pantothenic acid
folic acid
niacin
biotin

Cobalamin is the general name for vitamin B12.

What food source is the nutrient found in?
Vitamin B12 is found in animal foods, fortified foods, and some fermented foods. Some sources of B12 are:

eggs
meat
poultry
fish
dairy products
tempeh and miso, which both come from soy

How does the nutrient affect the body?
Vitamin B12 helps the body:

make red blood cells, with folic acid, another B-vitamin
work with many chemicals found in all body cells
copy the genetic code within each cell
form and maintain the nervous system
build and maintain protective coating around nerves
digest and use fats, carbohydrates, and some proteins for energy
form neurotransmitters in the brain, such as serotonin, that help regulate mood, sleep, and appetite